I think we have the same understanding of the case then. We seem to have a different conclusion on derivative works based on the original Mickey Mouse once it enters the public domain. I agree with you that modern Mickey would still be under copyright.

It's a bit of a moot point in my opinion, because I don't think anyone outside of Disney would even want to make more of 1928 Mickey. It's old. It's not popular. Maybe they'd use him for a cameo or for parody, but shows already do that anyway, regardless of the copyright [1].

[1] https://southpark.fandom.com/wiki/Mickey_Mouse