Except – The expiration date can be extended by just continuing to use the IP – Ever wondered why movies get remakes/reimaginings every 30 years or so? We meme about them being “Out of ideas”, but really it’s so they can hold down their copyright.

No, that's just wrong. At one point, early Marvel contracts had clauses that allowed the movie producer to keep the contract going if they continued to put out movies. When Marvel got big (post-Iron Man), they had been trying to claw back those contracts. That's why Fox kept putting out an X-Man movie every few years, and Sony kept putting out Spiderman.

But, that has nothing to do with copyrights, and all of the remakes are just shit that Hollywood does for memberberries.

Using an IP doesn't extend the date at which it becomes public. Movies get remakes etc because they want to make more money. Some movie companies have deals around IP with the original IP owner that revert if they don't use the IP, but that's separate from when the IP goes public. Mickey Mouse for example will become public domain in 2024 unless disney successfully lobby for the length of copyright to be extended (again).

https://www.theguardian.com/film/2022/jul/03/mickey-mouse-disney-copyright-expiry

Winnie the Pooh recently became public domain for example, which is how we got the god awful 18+ movie "blood and honey".

Sony for example have exclusive movie rights to the Spider-Man IP in perpetuity as long as they release a movie every 5.75 years at most, otherwise it reverts back to Marvel. That's why they keep rebooting it and releasing sequels no matter how garbage they are - it's better for them to release a trash movie that bombs than it is to lose the most valuable superhero IP in the world.

Now that Stan Lee is dead, however, there is a countdown set for when the Spider-Man IP becomes public domain, and no amount of movie or comic releases will delay that.