Keep looking up derived chain for Property.Get if it doesn't exist.

src/libraries/System.Private.Xml/src/System/Xml/Serialization/ReflectionXmlSerializationReader.cs

@@ -637,7 +637,7 @@ private static ReflectionXmlSerializationReaderHelper.SetMemberValueDelegate Get
             (Type, string) typeMemberNameTuple = (o.GetType(), memberName);
             if (!s_setMemberValueDelegateCache.TryGetValue(typeMemberNameTuple, out ReflectionXmlSerializationReaderHelper.SetMemberValueDelegate? result))
             {
-                MemberInfo memberInfo = ReflectionXmlSerializationHelper.GetMember(o.GetType(), memberName);
+                MemberInfo memberInfo = ReflectionXmlSerializationHelper.GetEffectiveSetInfo(o.GetType(), memberName);
                 Debug.Assert(memberInfo != null, "memberInfo could not be retrieved");
                 Type memberType;
                 if (memberInfo is PropertyInfo propInfo)

src/libraries/System.Private.Xml/src/System/Xml/Serialization/ReflectionXmlSerializationWriter.cs

@@ -649,7 +649,7 @@ private void WriteStructMethod(StructMapping mapping, string n, string? ns, obje
         [RequiresUnreferencedCode("Calls GetType on object")]
         private object? GetMemberValue(object o, string memberName)
         {
-            MemberInfo memberInfo = ReflectionXmlSerializationHelper.GetMember(o.GetType(), memberName);
+            MemberInfo memberInfo = ReflectionXmlSerializationHelper.GetEffectiveGetInfo(o.GetType(), memberName);
             object? memberValue = GetMemberValue(o, memberInfo);
             return memberValue;
         }
@@ -1356,7 +1356,7 @@ private enum WritePrimitiveMethodRequirement
     internal static class ReflectionXmlSerializationHelper
     {
         [RequiresUnreferencedCode("Reflects over base members")]
-        public static MemberInfo GetMember(Type declaringType, string memberName)
+        public static MemberInfo? GetMember(Type declaringType, string memberName, bool throwOnNotFound)
         {
             MemberInfo[] memberInfos = declaringType.GetMember(memberName);
             if (memberInfos == null || memberInfos.Length == 0)
@@ -1377,7 +1377,11 @@ public static MemberInfo GetMember(Type declaringType, string memberName)
 
                 if (!foundMatchedMember)
                 {
-                    throw new InvalidOperationException(SR.Format(SR.XmlInternalErrorDetails, $"Could not find member named {memberName} of type {declaringType}"));
+                    if (throwOnNotFound)
+                    {
+                        throw new InvalidOperationException(SR.Format(SR.XmlInternalErrorDetails, $"Could not find member named {memberName} of type {declaringType}"));
+                    }
+                    return null;
                 }
 
                 declaringType = currentType!;
@@ -1398,5 +1402,61 @@ public static MemberInfo GetMember(Type declaringType, string memberName)
 
             return memberInfo;
         }
+
+        [RequiresUnreferencedCode(XmlSerializer.TrimSerializationWarning)]
+        public static MemberInfo GetEffectiveGetInfo(Type declaringType, string memberName)
+        {
+            MemberInfo memberInfo = GetMember(declaringType, memberName, true)!;
+
+            // For properties, we might have a PropertyInfo that does not have a valid
+            // getter at this level of inheritance. If that's the case, we need to look
+            // up the chain to find the right PropertyInfo for the getter.
+            if (memberInfo is PropertyInfo propInfo && propInfo.GetMethod == null)
+            {
+                var parent = declaringType.BaseType;
+
+                while (parent != null)
+                {
+                    var mi = GetMember(parent, memberName, false);
+
+                    if (mi is PropertyInfo pi && pi.GetMethod != null && pi.PropertyType == propInfo.PropertyType)
+                    {
+                        return pi;
+                    }
+
+                    parent = parent.BaseType;
+                }
+            }
+
+            return memberInfo;
+        }
+
+        [RequiresUnreferencedCode(XmlSerializer.TrimSerializationWarning)]
+        public static MemberInfo GetEffectiveSetInfo(Type declaringType, string memberName)
+        {
+            MemberInfo memberInfo = GetMember(declaringType, memberName, true)!;
+
+            // For properties, we might have a PropertyInfo that does not have a valid
+            // setter at this level of inheritance. If that's the case, we need to look
+            // up the chain to find the right PropertyInfo for the setter.
+            if (memberInfo is PropertyInfo propInfo && propInfo.SetMethod == null)
+            {
+                var parent = declaringType.BaseType;
+
+                while (parent != null)
+                {
+                    var mi = GetMember(parent, memberName, false);
+
+                    if (mi is PropertyInfo pi && pi.SetMethod != null && pi.PropertyType == propInfo.PropertyType)
+                    {
+                        return pi;
+                    }
+
+                    parent = parent.BaseType;
+                }
+            }
+
+            return memberInfo;
+        }
     }
 }

src/libraries/System.Private.Xml/src/System/Xml/Serialization/Types.cs

@@ -1219,7 +1219,10 @@ private static bool ShouldBeReplaced(
                             replacedInfo = info;
                             if (replacedInfo != memberInfoToBeReplaced)
                             {
-                                if (!info.GetMethod!.IsPublic
+                                // The property name is a match. It might be an override, or
+                                // it might be hiding. Either way, check to see if the derived
+                                // property has a getter that is useable for serialization.
+                                if (info.GetMethod != null && !info.GetMethod!.IsPublic
                                     && memberInfoToBeReplaced is PropertyInfo
                                     && ((PropertyInfo)memberInfoToBeReplaced).GetMethod!.IsPublic
                                    )

src/libraries/System.Private.Xml/tests/XmlSerializer/XmlSerializerTests.RuntimeOnly.cs

@@ -2810,13 +2810,14 @@ public static void DerivedTypeWithDifferentOverrides()
     [Fact]
     public static void DerivedTypeWithDifferentOverrides2()
     {
-        DerivedTypeWithDifferentOverrides2 value = new DerivedTypeWithDifferentOverrides2() { Name1 = "Name1", Name2 = "Name2", Name3 = "Name3", Name4 = "Name4", Name5 = "Name5", Name6 = "Name6" };
+        DerivedTypeWithDifferentOverrides2 value = new DerivedTypeWithDifferentOverrides2() { Name1 = "Name1", Name2 = "Name2", Name3 = "Name3", Name4 = "Name4", Name5 = "Name5", Name6 = "Name6", Name7 = "Name7" };
         ((DerivedTypeWithDifferentOverrides)value).Name5 = "MidLevelName5";
         ((DerivedTypeWithDifferentOverrides)value).Name4 = "MidLevelName4";
         ((SerializationTypes.BaseType)value).Name4 = "BaseLevelName4";
         ((DerivedTypeWithDifferentOverrides)value).Name6 = "MidLevelName6";
         ((SerializationTypes.BaseType)value).Name6 = "BaseLevelName6";
-        DerivedTypeWithDifferentOverrides2 actual = SerializeAndDeserialize<DerivedTypeWithDifferentOverrides2>(value, @"<?xml version=""1.0""?><DerivedTypeWithDifferentOverrides2 xmlns:xsi=""http://www.w3.org/2001/XMLSchema-instance"" xmlns:xsd=""http://www.w3.org/2001/XMLSchema""><Name1>Name1</Name1><Name2>Name2</Name2><Name3>Name3</Name3><Name4>BaseLevelName4</Name4><Name5>MidLevelName5</Name5><Name6>BaseLevelName6</Name6></DerivedTypeWithDifferentOverrides2>");
+        ((DerivedTypeWithDifferentOverrides)value).Name7 = "MidLevelName7";
+        DerivedTypeWithDifferentOverrides2 actual = SerializeAndDeserialize<DerivedTypeWithDifferentOverrides2>(value, @"<?xml version=""1.0""?><DerivedTypeWithDifferentOverrides2 xmlns:xsi=""http://www.w3.org/2001/XMLSchema-instance"" xmlns:xsd=""http://www.w3.org/2001/XMLSchema""><Name1>Name1</Name1><Name2>Name2</Name2><Name3>Name3</Name3><Name4>BaseLevelName4</Name4><Name5>MidLevelName5</Name5><Name6>BaseLevelName6</Name6><Name7>MidLevelName7</Name7></DerivedTypeWithDifferentOverrides2>");
         Assert.Equal(value.Name1, actual.Name1);
         Assert.Equal(value.Name2, actual.Name2);
         Assert.Equal(value.Name3, actual.Name3);
@@ -2829,6 +2830,8 @@ public static void DerivedTypeWithDifferentOverrides2()
         Assert.Null(actual.Name6);
         Assert.Equal(((DerivedTypeWithDifferentOverrides)actual).Name6, ((SerializationTypes.BaseType)actual).Name6);
         Assert.Equal(((SerializationTypes.BaseType)actual).Name6, ((SerializationTypes.BaseType)actual).Name6);
+        Assert.Equal(((DerivedTypeWithDifferentOverrides)actual).Name7, ((SerializationTypes.BaseType)actual).Name7);
+        Assert.Equal(actual.Name7, ((SerializationTypes.BaseType)actual).Name7);
     }
 
     [Fact]

src/libraries/System.Runtime.Serialization.Xml/tests/DataContractSerializer.cs

@@ -1085,7 +1085,7 @@ public static void DCS_WithListOfXElement()
     public static void DCS_DerivedTypeWithDifferentOverrides()
     {
         var x = new DerivedTypeWithDifferentOverrides() { Name1 = "Name1", Name2 = "Name2", Name3 = "Name3", Name4 = "Name4", Name5 = "Name5" };
-        var y = DataContractSerializerHelper.SerializeAndDeserialize<DerivedTypeWithDifferentOverrides>(x, @"<DerivedTypeWithDifferentOverrides xmlns=""http://schemas.datacontract.org/2004/07/SerializationTypes"" xmlns:i=""http://www.w3.org/2001/XMLSchema-instance""><Name1>Name1</Name1><Name2 i:nil=""true""/><Name3 i:nil=""true""/><Name4 i:nil=""true""/><Name5 i:nil=""true""/><Name6 i:nil=""true""/><Name2>Name2</Name2><Name3>Name3</Name3><Name5>Name5</Name5></DerivedTypeWithDifferentOverrides>");
+        var y = DataContractSerializerHelper.SerializeAndDeserialize<DerivedTypeWithDifferentOverrides>(x, @"<DerivedTypeWithDifferentOverrides xmlns=""http://schemas.datacontract.org/2004/07/SerializationTypes"" xmlns:i=""http://www.w3.org/2001/XMLSchema-instance""><Name1>Name1</Name1><Name2 i:nil=""true""/><Name3 i:nil=""true""/><Name4 i:nil=""true""/><Name5 i:nil=""true""/><Name6 i:nil=""true""/><Name7 i:nil=""true""/><Name2>Name2</Name2><Name3>Name3</Name3><Name5>Name5</Name5></DerivedTypeWithDifferentOverrides>");
 
         Assert.Equal(x.Name1, y.Name1);
         Assert.Equal(x.Name2, y.Name2);

src/libraries/System.Runtime.Serialization.Xml/tests/SerializationTypes.RuntimeOnly.cs

@@ -837,6 +837,8 @@ public class BaseType
         public string @Name5 { get; set; }
 
         public virtual string Name6 { get; set; }
+
+        public virtual string Name7 { get; set; }
     }
 
     public class DerivedTypeWithDifferentOverrides : BaseType
@@ -852,6 +854,8 @@ public class DerivedTypeWithDifferentOverrides : BaseType
         public new string Name5 { get; set; }
 
         public override string Name6 { get; set; }
+
+        public override string Name7 { set { base.Name7 = value; } }
     }
 
     public class DerivedTypeWithDifferentOverrides2 : DerivedTypeWithDifferentOverrides