@alexandra
FWIW, FairEmail (Android) supports OAuth2, with the caveat that Google doesn't let the F-Droid build use OAuth2. You'd need to use either the GitHub release (which automatically checks for updates) or the Play Store version.
Might be useful as a stop-gap if you aren't fully migrated by the 30th.
@Parienve@qoto.org I neither use Android nor want to use a stop-gap, worst case I'll autoforward everything to my server.