You can’t do Extras for TV Shows that way. <—TV Show Extras go into Season 00/Special Folders.
You can do Extras for Movies that way… providing you are Naming/Structuring Extras Correctly:
https://support.plex.tv/articles/local-files-for-trailers-and-extras/
BTW:
Here’s the pain point for TV Show Extras:
… you can add your vote - and/or you can start creating Special Seasons - like the rest of us.
