I only discovered tonight about this, or I would have posted on January 1, when it happened:
As a result of the accession of the United States to the Berne Convention, WIPO Intellectual Property treaties, and the Sonny Bono Copyright Term Extension Act, copyright in the United States lasts for the life of the author + 70 years, or 95 years for a corporate created work. This meant, that it wasn't until January 1, 2024, that the copyright on the film
Steamboat Willie expired, which also means the copyright on Mickey and Minnie Mouse also expired. Thus, the copyright on Mickey Mouse (and Minnie too!) died at 11:59:59 P.M., December 31, 2023.
The now dead copyright is survived by The Walt Disney Company, who pissed off enough people when they got the last copyright extension, that it was decided that no more copyright extensions would be granted.