The first solution is probably the laziest, but it’s definitely the simplest. Marvel can just say that mutants have existed in the MCU this whole time, and we just haven’t heard about them before.

From the get-go, you can already see there are a lot of problems when it comes to this approach. For one, the issue with mutants has always been societal, and the clash with mutants and humans have always been huge. With no mention of mutants in the past 23 movies, it just doesn’t seem realistic that mutants have been there for a long time.

Then again, maybe they can say that the mutants are only getting attention now since more of them are starting to surface. I think they can write in a line which says the mutant issue has been largely ignored thanks to the over-the-top antics of the Avengers. I mean, if Wakanda can exist this whole time, only being introduced in Phase 3, then maybe they can do the same with the mutants.

Again, it’s not the most clever solution, but it’s definitely the simplest.