The problem with OAuth and Google is that Google requires from 3rd party vendors verification and it's very hard to obtain. Unsurprisingly, Google rejects requests for verification without any explanation and ignores any follow up communication.
Not sure, I know that newer versions of thunderbird and k9 do, but you may need remove the account and re-create it; I didn't test changing the settings myself, I just deleted the old accounts and re-created them as IMAP / oauth.
https://developers.google.com/gmail/imap/xoauth2-protocol