I'm pretty sure, at least in the USA, there have been rulings that there must be human authorship for something to have copyright protection. This has happened both in the courts and the US Copyright Office has spoken on the matter as well. If you're interested in one of the court cases I'd suggest looking up Thaler v. Perlmutter.

There was a stipulation though, any human made parts of a work is copyrightable, so in your scenario of copying a movie would probably still be illegal unless the entire movie was created by gen ai, but it would seem that you could probably cut the gen ai bits and release and reuse them without violating any copyright, but I'm also not a lawyer so...