Problem with movie extras

[Efficient_Good_5784]

This does NOT mean that I can keep the movie and extras in the same folder as ALL OTHER movies (my desire) but I have to create a specific folder for that movie, anyway.
SAD thing, I don't want a million folders...

The amount of folders should not affect the performance of using Jellyfin. You wont even have to see the media and their folders as you'll be accessing the media through Jellyfin's GUI and not a file browser.
As you discovered, Jellyfin will need each movie and its extras to be in their own movie subfolder for the extras to be picked up without having them in yet another subfolder.

Also something that you might want to know. As a single folder starts growing in size (amount of items it contains), your OS will start struggling to open it and navigate through it. As in, it will eventually start taking more time to load the directory properly.