Well no, that's not the only solution to the problem. It's not even the best solution. I don't want collections-within-collections, I want the Santa Clause movies to exist individually in different collections but not in the main view.

If a movie exists in a "hidden from main view" collection, then it should always be hidden from the main view.

If a movie exists in a "hidden from main view" collection AND a "shown in main view" collection, then it should still be hidden from main view, but allowed in both collections.

This is currently how Plex already works - you can add a movie to as many "hidden from main view" collections as you want, and it will appear in them all, with no issues.

The solution is simple. If you have a collection set to "show movies in main view", then Plex should show these movies in the main view unless they exist in a collection where they supposed to be hidden from main view.