There is an example TiddlyWiki5/plugins/tiddlywiki/async/files at master · TiddlyWiki/TiddlyWiki5 · GitHub
If you use the tiddlywiki xx --build command, it automatically uses everything that is part of the tiddlers or plugins folder. If in one of the plugins folder, there is a tiddlywiki.files file, it only uses the content, that is defined in that file. It’s a “all or nothing” behaviour.
This makes it possible to exclude plugins from being built, if an empty tiddlywiki.files file is used.
I did rewrite the Plugins docs: https://tiddlywiki.com/#Plugins:Plugins%20[[Installing%20custom%20plugins%20on%20Node.js]]%20PluginFolders to work for a video series I did lately.
That may help too: