On January 1, 2024, Mickey Mouse entered the public domain, meaning that anybody can now technically use him in whatever movie, TV show, book, video game or porno flick they want.
There are limits, of course. Disney remains litigious, and may find ways to bring legal action against people who use Mickey in ways they don't like even though Disney's copyright on the character has expired; they may use trademark law rather than copyright law, for example. Also, the only version of Mickey now in the public domain is the very first one that appeared in Steamboat Willie, the 1928 short cartoon that introduced the world to the iconic mouse. Using any other version is as forbidden as it's always been.
Under U.S. law, any property introduced before 1978 goes into the public domain 95 years after the date of publication. And there are characters introduced around the same time as Mickey who will soon be in there, characters like Superman and Batman.
Superman will be in the public domain in 2034
Superman first appeared in 1938, in Action Comics #1. That means he'll be in the public domain in 2034, just a decade in the future.
Batman will be in the public domain in 2035
Meanwhile, Batman was introduced in Detective Comics #27 in 1939. That means he'll be in the public domain in 2035, a year after Superman.
The same restrictions that apply to Mickey will apply to Superman and Batman when their time comes. People will only be able to use the first-ever versions of the characters, and there's nothing to say that DC won't still find ways to go after people it thinks are misusing the characters. Still, the prospect of having the world's two most famous superheroes in the public domain is tantalizing. Technically, someone could make a Batman fan film and get it released in theaters without breaking the law, although the particulars may get dicey.