I had to deal with this last spring. I finally got things working again with mbsync, msmtp, mu/mu4e, and for the oauth stuff, pizauth. This combination has worked well for me ever since. Most of the details can be found at
https://brettpresnell.com/post/email/ I am still using an early version of pizauth, so it's possible that the details of setting it up may have changed a bit.
