https://tiddlywiki.com/static/External%2520Attachments%2520Plugin.html
The External Attachments Plugin provides support for importing tiddlers as external attachments. That means that instead of importing binary files as self-contained tiddlers, they are imported as "skinny" tiddlers that reference the original file via the _canonical_uri field. This reduces the size of the wiki and thus improves performance. However, it does mean that the wiki is no longer fully self-contained.
This plugin only works when using TiddlyWiki with platforms such as TiddlyDesktop that support the path attribute for imported/dragged files.
This plugin is a fork of https://github.com/Jermolene/TiddlyWiki5/tree/d4846bae6c7e0e529d62cf83d439528ad63aa003/plugins/tiddlywiki/external-attachments
Just install it from CPL, and reload page.
Then drag&drop file into TidGi will create a skinny tiddler. Try edit that tiddler to find out how this "pointer file" works.
TidGi supports link and _canonical_uri to use file:// prefix (or open://, both works the same), for example:
[ext[Some External File Link with CJK character|file:///Users/linonetwo/Downloads/(OCRed)奖励的惩罚 (（美）科恩著) (Z-Library).pdf]]
[ext[An External Folder Link|file:///Users/linonetwo/Downloads/]]So when you drag a file into wiki, _canonical_uri created by this plugin will also prefixed by file://.