diff --git a/packages/react-dom/src/events/SyntheticEvent.js b/packages/react-dom/src/events/SyntheticEvent.js
index 0da906d712890..87bdad3548cdc 100644
--- a/packages/react-dom/src/events/SyntheticEvent.js
+++ b/packages/react-dom/src/events/SyntheticEvent.js
@@ -9,6 +9,8 @@
 
 /* eslint valid-typeof: 0 */
 
+import type {Fiber} from 'react-reconciler/src/ReactInternalTypes';
+
 import assign from 'shared/assign';
 import getEventCharCode from './getEventCharCode';
 
@@ -44,7 +46,7 @@ function createSyntheticEvent(Interface: EventInterfaceType) {
   function SyntheticBaseEvent(
     reactName: string | null,
     reactEventType: string,
-    targetInst: Fiber,
+    targetInst: Fiber | null,
     nativeEvent: {[propName: string]: mixed, ...},
     nativeEventTarget: null | EventTarget,
   ) {
diff --git a/packages/react-dom/src/events/plugins/BeforeInputEventPlugin.js b/packages/react-dom/src/events/plugins/BeforeInputEventPlugin.js
index 5e413a3459e14..c9f18c6abf7c4 100644
--- a/packages/react-dom/src/events/plugins/BeforeInputEventPlugin.js
+++ b/packages/react-dom/src/events/plugins/BeforeInputEventPlugin.js
@@ -12,6 +12,7 @@ import type {Fiber} from 'react-reconciler/src/ReactInternalTypes';
 import type {AnyNativeEvent} from '../../events/PluginModuleType';
 import type {DispatchQueue} from '../DOMPluginEventSystem';
 import type {EventSystemFlags} from '../EventSystemFlags';
+import type {ReactSyntheticEvent} from '../ReactSyntheticEventType';
 
 import {canUseDOM} from 'shared/ExecutionEnvironment';
 
@@ -228,7 +229,8 @@ function extractCompositionEvent(
 
   const listeners = accumulateTwoPhaseListeners(targetInst, eventType);
   if (listeners.length > 0) {
-    const event = new SyntheticCompositionEvent(
+    // $FlowFixMe[incompatible-type]
+    const event: ReactSyntheticEvent = new SyntheticCompositionEvent(
       eventType,
       domEventName,
       null,
@@ -239,10 +241,12 @@ function extractCompositionEvent(
     if (fallbackData) {
       // Inject data generated from fallback path into the synthetic event.
       // This matches the property of native CompositionEventInterface.
+      // $FlowFixMe[incompatible-use]
       event.data = fallbackData;
     } else {
       const customData = getDataFromCustomEvent(nativeEvent);
       if (customData !== null) {
+        // $FlowFixMe[incompatible-use]
         event.data = customData;
       }
     }
@@ -398,7 +402,8 @@ function extractBeforeInputEvent(
 
   const listeners = accumulateTwoPhaseListeners(targetInst, 'onBeforeInput');
   if (listeners.length > 0) {
-    const event = new SyntheticInputEvent(
+    // $FlowFixMe[incompatible-type]
+    const event: ReactSyntheticEvent = new SyntheticInputEvent(
       'onBeforeInput',
       'beforeinput',
       null,
@@ -406,6 +411,7 @@ function extractBeforeInputEvent(
       nativeEventTarget,
     );
     dispatchQueue.push({event, listeners});
+    // $FlowFixMe[incompatible-use]
     event.data = chars;
   }
 }
diff --git a/packages/react-dom/src/events/plugins/ChangeEventPlugin.js b/packages/react-dom/src/events/plugins/ChangeEventPlugin.js
index 8985c50c71f9a..cc99bd3ad1264 100644
--- a/packages/react-dom/src/events/plugins/ChangeEventPlugin.js
+++ b/packages/react-dom/src/events/plugins/ChangeEventPlugin.js
@@ -10,6 +10,8 @@ import type {AnyNativeEvent} from '../PluginModuleType';
 import type {DOMEventName} from '../DOMEventNames';
 import type {DispatchQueue} from '../DOMPluginEventSystem';
 import type {EventSystemFlags} from '../EventSystemFlags';
+import type {Fiber} from 'react-reconciler/src/ReactInternalTypes';
+import type {ReactSyntheticEvent} from '../ReactSyntheticEventType';
 
 import {registerTwoPhaseEvent} from '../EventRegistry';
 import {SyntheticEvent} from '../SyntheticEvent';
@@ -57,7 +59,8 @@ function createAndAccumulateChangeEvent(
   enqueueStateRestore(((target: any): Node));
   const listeners = accumulateTwoPhaseListeners(inst, 'onChange');
   if (listeners.length > 0) {
-    const event = new SyntheticEvent(
+    // $FlowFixMe[incompatible-type]
+    const event: ReactSyntheticEvent = new SyntheticEvent(
       'onChange',
       'change',
       null,
diff --git a/packages/react-dom/src/events/plugins/EnterLeaveEventPlugin.js b/packages/react-dom/src/events/plugins/EnterLeaveEventPlugin.js
index ea7e3fac1cd57..ef90afcec0414 100644
--- a/packages/react-dom/src/events/plugins/EnterLeaveEventPlugin.js
+++ b/packages/react-dom/src/events/plugins/EnterLeaveEventPlugin.js
@@ -11,6 +11,8 @@ import type {AnyNativeEvent} from '../PluginModuleType';
 import type {DOMEventName} from '../DOMEventNames';
 import type {DispatchQueue} from '../DOMPluginEventSystem';
 import type {EventSystemFlags} from '../EventSystemFlags';
+import type {Fiber} from 'react-reconciler/src/ReactInternalTypes';
+import type {KnownReactSyntheticEvent} from '../ReactSyntheticEventType';
 
 import {registerDirectEvent} from '../EventRegistry';
 import {isReplayingEvent} from '../CurrentReplayingEvent';
@@ -21,7 +23,6 @@ import {
   isContainerMarkedAsRoot,
 } from '../../client/ReactDOMComponentTree';
 import {accumulateEnterLeaveTwoPhaseListeners} from '../DOMPluginEventSystem';
-import type {KnownReactSyntheticEvent} from '../ReactSyntheticEventType';
 
 import {HostComponent, HostText} from 'react-reconciler/src/ReactWorkTags';
 import {getNearestMountedFiber} from 'react-reconciler/src/ReactFiberTreeReflection';
@@ -133,7 +134,9 @@ function extractEvents(
   const fromNode = from == null ? win : getNodeFromInstance(from);
   const toNode = to == null ? win : getNodeFromInstance(to);
 
-  const leave = new SyntheticEventCtor(
+  // $FlowFixMe[prop-missing]
+  // $FlowFixMe[incompatible-type]
+  const leave: KnownReactSyntheticEvent = new SyntheticEventCtor(
     leaveEventType,
     eventTypePrefix + 'leave',
     from,
@@ -149,6 +152,7 @@ function extractEvents(
   // the first ancestor. Next time, we will ignore the event.
   const nativeTargetInst = getClosestInstanceFromNode((nativeEventTarget: any));
   if (nativeTargetInst === targetInst) {
+    // $FlowFixMe[prop-missing]
     const enterEvent: KnownReactSyntheticEvent = new SyntheticEventCtor(
       enterEventType,
       eventTypePrefix + 'enter',
diff --git a/packages/react-dom/src/events/plugins/SelectEventPlugin.js b/packages/react-dom/src/events/plugins/SelectEventPlugin.js
index befa735be8788..2032b02565329 100644
--- a/packages/react-dom/src/events/plugins/SelectEventPlugin.js
+++ b/packages/react-dom/src/events/plugins/SelectEventPlugin.js
@@ -11,6 +11,8 @@ import type {AnyNativeEvent} from '../PluginModuleType';
 import type {DOMEventName} from '../DOMEventNames';
 import type {DispatchQueue} from '../DOMPluginEventSystem';
 import type {EventSystemFlags} from '../EventSystemFlags';
+import type {Fiber} from 'react-reconciler/src/ReactInternalTypes';
+import type {ReactSyntheticEvent} from '../ReactSyntheticEventType';
 
 import {canUseDOM} from 'shared/ExecutionEnvironment';
 import {SyntheticEvent} from '../../events/SyntheticEvent';
@@ -114,7 +116,8 @@ function constructSelectEvent(dispatchQueue, nativeEvent, nativeEventTarget) {
       'onSelect',
     );
     if (listeners.length > 0) {
-      const event = new SyntheticEvent(
+      // $FlowFixMe[incompatible-type]
+      const event: ReactSyntheticEvent = new SyntheticEvent(
         'onSelect',
         'select',
         null,
diff --git a/packages/react-dom/src/events/plugins/SimpleEventPlugin.js b/packages/react-dom/src/events/plugins/SimpleEventPlugin.js
index 03bf9484b2c04..07c9ec94c7104 100644
--- a/packages/react-dom/src/events/plugins/SimpleEventPlugin.js
+++ b/packages/react-dom/src/events/plugins/SimpleEventPlugin.js
@@ -12,6 +12,7 @@ import type {Fiber} from 'react-reconciler/src/ReactInternalTypes';
 import type {AnyNativeEvent} from '../../events/PluginModuleType';
 import type {DispatchQueue} from '../DOMPluginEventSystem';
 import type {EventSystemFlags} from '../EventSystemFlags';
+import type {ReactSyntheticEvent} from '../ReactSyntheticEventType';
 
 import {
   SyntheticEvent,
@@ -172,7 +173,8 @@ function extractEvents(
     );
     if (listeners.length > 0) {
       // Intentionally create event lazily.
-      const event = new SyntheticEventCtor(
+      // $FlowFixMe[incompatible-type]
+      const event: ReactSyntheticEvent = new SyntheticEventCtor(
         reactName,
         reactEventType,
         null,
@@ -204,7 +206,8 @@ function extractEvents(
     );
     if (listeners.length > 0) {
       // Intentionally create event lazily.
-      const event = new SyntheticEventCtor(
+      // $FlowFixMe[incompatible-type]
+      const event: ReactSyntheticEvent = new SyntheticEventCtor(
         reactName,
         reactEventType,
         null,
diff --git a/packages/react-native-renderer/src/ReactFabricEventEmitter.js b/packages/react-native-renderer/src/ReactFabricEventEmitter.js
index c3b89e91779a3..12ba859bf70f4 100644
--- a/packages/react-native-renderer/src/ReactFabricEventEmitter.js
+++ b/packages/react-native-renderer/src/ReactFabricEventEmitter.js
@@ -11,7 +11,10 @@ import type {AnyNativeEvent} from './legacy-events/PluginModuleType';
 import type {Fiber} from 'react-reconciler/src/ReactInternalTypes';
 import type {LegacyPluginModule} from './legacy-events/PluginModuleType';
 import type {ReactSyntheticEvent} from './legacy-events/ReactSyntheticEventType';
-import type {TopLevelType} from './legacy-events/TopLevelEventTypes';
+import type {
+  RNTopLevelEventType,
+  TopLevelType,
+} from './legacy-events/TopLevelEventTypes';
 
 import {registrationNameModules} from './legacy-events/EventPluginRegistry';
 import {batchedUpdates} from './legacy-events/ReactGenericBatching';
diff --git a/packages/react-reconciler/src/ReactFiberCacheComponent.new.js b/packages/react-reconciler/src/ReactFiberCacheComponent.new.js
index 2552ca7a4fa96..92c4f60450737 100644
--- a/packages/react-reconciler/src/ReactFiberCacheComponent.new.js
+++ b/packages/react-reconciler/src/ReactFiberCacheComponent.new.js
@@ -8,6 +8,7 @@
  */
 
 import type {ReactContext} from 'shared/ReactTypes';
+import type {Fiber} from 'react-reconciler/src/ReactInternalTypes';
 
 import {enableCache} from 'shared/ReactFeatureFlags';
 import {REACT_CONTEXT_TYPE} from 'shared/ReactSymbols';
diff --git a/packages/react-reconciler/src/ReactFiberCacheComponent.old.js b/packages/react-reconciler/src/ReactFiberCacheComponent.old.js
index 1fd8c144bc5ec..1955b22e9f76d 100644
--- a/packages/react-reconciler/src/ReactFiberCacheComponent.old.js
+++ b/packages/react-reconciler/src/ReactFiberCacheComponent.old.js
@@ -8,6 +8,7 @@
  */
 
 import type {ReactContext} from 'shared/ReactTypes';
+import type {Fiber} from 'react-reconciler/src/ReactInternalTypes';
 
 import {enableCache} from 'shared/ReactFeatureFlags';
 import {REACT_CONTEXT_TYPE} from 'shared/ReactSymbols';
diff --git a/packages/react-reconciler/src/ReactFiberConcurrentUpdates.new.js b/packages/react-reconciler/src/ReactFiberConcurrentUpdates.new.js
index e496389782025..6b1ecbde7f018 100644
--- a/packages/react-reconciler/src/ReactFiberConcurrentUpdates.new.js
+++ b/packages/react-reconciler/src/ReactFiberConcurrentUpdates.new.js
@@ -7,7 +7,7 @@
  * @flow
  */
 
-import type {FiberRoot} from './ReactInternalTypes';
+import type {Fiber, FiberRoot} from './ReactInternalTypes';
 import type {
   UpdateQueue as HookQueue,
   Update as HookUpdate,
diff --git a/packages/react-reconciler/src/ReactFiberConcurrentUpdates.old.js b/packages/react-reconciler/src/ReactFiberConcurrentUpdates.old.js
index 7dd87358cf6a1..798506fd9b5ea 100644
--- a/packages/react-reconciler/src/ReactFiberConcurrentUpdates.old.js
+++ b/packages/react-reconciler/src/ReactFiberConcurrentUpdates.old.js
@@ -7,7 +7,7 @@
  * @flow
  */
 
-import type {FiberRoot} from './ReactInternalTypes';
+import type {Fiber, FiberRoot} from './ReactInternalTypes';
 import type {
   UpdateQueue as HookQueue,
   Update as HookUpdate,
diff --git a/packages/react-reconciler/src/ReactFiberLane.new.js b/packages/react-reconciler/src/ReactFiberLane.new.js
index 4aebeba7a205e..2dcbe70ee7960 100644
--- a/packages/react-reconciler/src/ReactFiberLane.new.js
+++ b/packages/react-reconciler/src/ReactFiberLane.new.js
@@ -7,7 +7,7 @@
  * @flow
  */
 
-import type {FiberRoot} from './ReactInternalTypes';
+import type {Fiber, FiberRoot} from './ReactInternalTypes';
 import type {Transition} from './ReactFiberTracingMarkerComponent.new';
 import type {ConcurrentUpdate} from './ReactFiberConcurrentUpdates.new';
 
diff --git a/packages/react-reconciler/src/ReactFiberLane.old.js b/packages/react-reconciler/src/ReactFiberLane.old.js
index 5861e9d3d3252..6042a1a31c429 100644
--- a/packages/react-reconciler/src/ReactFiberLane.old.js
+++ b/packages/react-reconciler/src/ReactFiberLane.old.js
@@ -7,7 +7,7 @@
  * @flow
  */
 
-import type {FiberRoot} from './ReactInternalTypes';
+import type {Fiber, FiberRoot} from './ReactInternalTypes';
 import type {Transition} from './ReactFiberTracingMarkerComponent.old';
 import type {ConcurrentUpdate} from './ReactFiberConcurrentUpdates.old';
 
diff --git a/packages/react-reconciler/src/ReactFiberTransition.new.js b/packages/react-reconciler/src/ReactFiberTransition.new.js
index 527cb89877f62..c095c8e54f14a 100644
--- a/packages/react-reconciler/src/ReactFiberTransition.new.js
+++ b/packages/react-reconciler/src/ReactFiberTransition.new.js
@@ -6,7 +6,7 @@
  *
  * @flow
  */
-import type {FiberRoot} from './ReactInternalTypes';
+import type {Fiber, FiberRoot} from './ReactInternalTypes';
 import type {Lanes} from './ReactFiberLane.new';
 import type {StackCursor} from './ReactFiberStack.new';
 import type {Cache, SpawnedCachePool} from './ReactFiberCacheComponent.new';
diff --git a/packages/react-reconciler/src/ReactFiberTransition.old.js b/packages/react-reconciler/src/ReactFiberTransition.old.js
index 8323559d58f8b..30c2ecfd4ea6c 100644
--- a/packages/react-reconciler/src/ReactFiberTransition.old.js
+++ b/packages/react-reconciler/src/ReactFiberTransition.old.js
@@ -6,7 +6,7 @@
  *
  * @flow
  */
-import type {FiberRoot} from './ReactInternalTypes';
+import type {Fiber, FiberRoot} from './ReactInternalTypes';
 import type {Lanes} from './ReactFiberLane.old';
 import type {StackCursor} from './ReactFiberStack.old';
 import type {Cache, SpawnedCachePool} from './ReactFiberCacheComponent.old';
diff --git a/packages/react-reconciler/src/ReactFiberTransitionPool.old.js b/packages/react-reconciler/src/ReactFiberTransitionPool.old.js
index e78670aa3f94f..e89c798be1f95 100644
--- a/packages/react-reconciler/src/ReactFiberTransitionPool.old.js
+++ b/packages/react-reconciler/src/ReactFiberTransitionPool.old.js
@@ -6,7 +6,7 @@
  *
  * @flow
  */
-import type {FiberRoot} from './ReactInternalTypes';
+import type {Fiber, FiberRoot} from './ReactInternalTypes';
 import type {Lanes} from './ReactFiberLane.old';
 import type {StackCursor} from './ReactFiberStack.old';
 import type {Cache, SpawnedCachePool} from './ReactFiberCacheComponent.old';
diff --git a/packages/react-reconciler/src/ReactFiberTreeContext.new.js b/packages/react-reconciler/src/ReactFiberTreeContext.new.js
index f9c5104ed6b13..f1c23f61b5a42 100644
--- a/packages/react-reconciler/src/ReactFiberTreeContext.new.js
+++ b/packages/react-reconciler/src/ReactFiberTreeContext.new.js
@@ -60,6 +60,8 @@
 // log2(32) = 5 bits. That means we can lop bits off the end 5 at a time without
 // affecting the final result.
 
+import type {Fiber} from 'react-reconciler/src/ReactInternalTypes';
+
 import {getIsHydrating} from './ReactFiberHydrationContext.new';
 import {clz32} from './clz32';
 import {Forked, NoFlags} from './ReactFiberFlags';
diff --git a/packages/react-reconciler/src/ReactFiberTreeContext.old.js b/packages/react-reconciler/src/ReactFiberTreeContext.old.js
index 840335d00c4e4..69d7f75dbac1d 100644
--- a/packages/react-reconciler/src/ReactFiberTreeContext.old.js
+++ b/packages/react-reconciler/src/ReactFiberTreeContext.old.js
@@ -60,6 +60,8 @@
 // log2(32) = 5 bits. That means we can lop bits off the end 5 at a time without
 // affecting the final result.
 
+import type {Fiber} from 'react-reconciler/src/ReactInternalTypes';
+
 import {getIsHydrating} from './ReactFiberHydrationContext.old';
 import {clz32} from './clz32';
 import {Forked, NoFlags} from './ReactFiberFlags';
diff --git a/packages/react-reconciler/src/getComponentNameFromFiber.js b/packages/react-reconciler/src/getComponentNameFromFiber.js
index 979914b7c4ba5..883ac838b975d 100644
--- a/packages/react-reconciler/src/getComponentNameFromFiber.js
+++ b/packages/react-reconciler/src/getComponentNameFromFiber.js
@@ -8,6 +8,7 @@
  */
 
 import type {ReactContext, ReactProviderType} from 'shared/ReactTypes';
+import type {Fiber} from './ReactInternalTypes';
 
 import {enableLegacyHidden} from 'shared/ReactFeatureFlags';
 
diff --git a/packages/shared/ReactTypes.js b/packages/shared/ReactTypes.js
index 6b36a7bdffd94..5ef83306706af 100644
--- a/packages/shared/ReactTypes.js
+++ b/packages/shared/ReactTypes.js
@@ -7,6 +7,8 @@
  * @flow
  */
 
+import type {Fiber} from 'react-reconciler/src/ReactInternalTypes';
+
 export type ReactNode =
   | React$Element<any>
   | ReactPortal
diff --git a/scripts/flow/react-native-host-hooks.js b/scripts/flow/react-native-host-hooks.js
index 083b9f6e0f098..86f5cabe7400c 100644
--- a/scripts/flow/react-native-host-hooks.js
+++ b/scripts/flow/react-native-host-hooks.js
@@ -9,16 +9,21 @@
 
 /* eslint-disable */
 
-import type {
-  MeasureOnSuccessCallback,
-  MeasureInWindowOnSuccessCallback,
-  MeasureLayoutOnSuccessCallback,
-  ReactNativeBaseComponentViewConfig,
-  ViewConfigGetter,
-} from 'react-native-renderer/src/ReactNativeTypes';
-import type {RNTopLevelEventType} from 'react-native-renderer/src/legacy-events/TopLevelEventTypes';
-import type {CapturedError} from 'react-reconciler/src/ReactCapturedValue';
-import type {Fiber} from 'react-reconciler/src/ReactInternalTypes';
+// libdefs cannot actually import. These are supposed to be the types imported
+// from 'react-native-renderer/src/ReactNativeTypes'
+type __MeasureOnSuccessCallback = any;
+type __MeasureInWindowOnSuccessCallback = any;
+type __MeasureLayoutOnSuccessCallback = any;
+type __ReactNativeBaseComponentViewConfig = any;
+type __ViewConfigGetter = any;
+
+// libdefs cannot actually import. This is supposed to be the type imported
+// from 'react-native-renderer/src/legacy-events/TopLevelEventTypes';
+type __RNTopLevelEventType = any;
+
+// libdefs cannot actually import. This is supposed to be the type imported
+// from 'react-reconciler/src/ReactCapturedValue'
+type __CapturedError = any;
 
 type DeepDifferOptions = {+unsafelyIgnoreFunctions?: boolean};
 type RawEventEmitterEvent = $ReadOnly<{
@@ -53,7 +58,7 @@ declare module 'react-native/Libraries/ReactPrivate/ReactNativePrivateInterface'
     ...
   };
   declare export var ReactFiberErrorDialog: {
-    showErrorDialog: (error: CapturedError) => boolean,
+    showErrorDialog: (error: __CapturedError) => boolean,
     ...
   };
   declare export var Platform: {OS: string, ...};
@@ -130,8 +135,8 @@ declare module 'react-native/Libraries/ReactPrivate/ReactNativePrivateInterface'
     customDirectEventTypes: Object,
     eventTypes: Object,
 
-    register: (name: string, callback: ViewConfigGetter) => string,
-    get: (name: string) => ReactNativeBaseComponentViewConfig,
+    register: (name: string, callback: __ViewConfigGetter) => string,
+    get: (name: string) => __ReactNativeBaseComponentViewConfig,
     ...
   };
   declare export var RawEventEmitter: {
@@ -166,7 +171,7 @@ declare var nativeFabricUIManager: {
   registerEventHandler: (
     callback: (
       eventTarget: null | Object,
-      type: RNTopLevelEventType,
+      type: __RNTopLevelEventType,
       payload: Object,
     ) => void,
   ) => void,
@@ -174,22 +179,22 @@ declare var nativeFabricUIManager: {
   dispatchCommand: (node: Object, command: string, args: Array<any>) => void,
   sendAccessibilityEvent: (node: Object, eventTypeName: string) => void,
 
-  measure: (node: Node, callback: MeasureOnSuccessCallback) => void,
+  measure: (node: Node, callback: __MeasureOnSuccessCallback) => void,
   measureInWindow: (
     node: Node,
-    callback: MeasureInWindowOnSuccessCallback,
+    callback: __MeasureInWindowOnSuccessCallback,
   ) => void,
   measureLayout: (
     node: Node,
     relativeNode: Node,
     onFail: () => void,
-    onSuccess: MeasureLayoutOnSuccessCallback,
+    onSuccess: __MeasureLayoutOnSuccessCallback,
   ) => void,
   findNodeAtPoint: (
     node: Node,
     locationX: number,
     locationY: number,
-    callback: (Fiber) => void,
+    callback: (Object) => void,
   ) => void,
   setIsJSResponder: (
     node: Node,