"authorization error" and can not access email account; oauth2 worked, but stopped.

I update Thunderbird/linux to v.130 over a year ago, implementing oath2 with gmail. I do NOT want to do more updates because with each previous update I lose desired capabilities; I did this update only because of gmail's authorization requirements. Worked fine for a while and then I started getting "authorization error" messages and could no longer access this account with Thunderbird. I have over 20gb of stored messages on my computer and do not want to do anything that will jeopardize this -- I generally delete all messages at the server. Google is of no help other than suggesting deleting and then somehow restarting the account. No. Someone suggested switching the account from oauth2 to password and then switching back again, but I am reluctant to do anything that might lose my messages. I can backup the entire profile, of course, but that just gets me back to where I was. I went through the reauthorization process with gmail, including getting the 6-digit code, but the error still exists. I've been forwarding mail in this account to another account, but I'd rather go back to the REAL account. Help!