As far as I can tell, Disney has not (yet) made any recent push for copyright extensions. Which would mean that their Steamboat Willie
cartoon will fall into public domain in 1 January 2024.
After that, things get complicated. People could make Mickey cartoons based on Steamboat Willie
, but they cannot use the Mickey from the Sorcerer's Apprentice
short or The Mickey Mouse Clubhouse
, as those copyrights are still protected. Of course, Disney will still have the trademark for Mickey Mouse and will likely use that for any potential legal battles.
Sherlock Holmes is currently in this grey area, with most of the early works are in public domain, but the last 10 stories (and their content) are protected.