I've moved to Migadu a few years ago for more or less the same reason, but pre AI - Google's unrequested filtering and sorting made things actively worse on my daily chaos. Moreover the eternal threat of Google cutting the cord for any non-defined infraction and locking you out of your own life is crazy. I still use drive and other Google features, but my email is just an account login and nothing more.

Migadu has been a breeze, very sane and transparent payment model, human support, infinite domains and accounts (!). What I really miss are calendar features which are just underdeveloped, but it seems mostly the Microsoft and Google have ruined that area by doing whatever they want.

I like the instructions Migadu gave for copying your emails over - just open thunderbird and copy or move everything from one account. I put everything in an Archive folder so can find it if ever needed. Just insanely pragmatic and it worked.