After ruining copyright law and borrowing from public domain works, Disney finally loses a property to public domain. An incredible start to the new year!
Disney has been using Steamboat Willy in the beginning credits of their shows/movies for a while now. They are attempting to make it a Trademark (since the copyright wouldn't be extended further). Since Trademarks must be defended, Disney will likely start suing anyone using Steamboat Willy on grounds of Trademark violation.
IP law is literally holding humanity back from progress its so infuriating. It was created with the good intentions for people to be able to profit from their inventions and creativity, but has been bastardized by corporations to have strangleholds on innovations that could benefit all of humanity yet profit matters more than people in this Capitalist hell scape.
Trademarks only matter if the intention or effect is to impersonate the business. If you started makeing feature length movies and used Steamboat Willy in the opening to trick customers into thinking it was a Disney movie they might be able to sue, but otherwise trademark doesn’t work that way.