I have not tried to set up a gmasil in 128, but I am having no issues with oauth generally with gmail. Why are you creating a new account in Thunderbird? Is there some issue with the update, or is it just today you needed to add an account.

I'm just setting up a new windows laptop. This was the first attempt to add gmail to Thunderbird 128 - it's not upgrading from any previous installation. I'm using the same M$ account and nothing was there when I installed it on this computer. Should there be?

The error I receive from google is: "400. That’s an error.

The server cannot process the request because it is malformed. It should not be retried. That’s all we know."

I've had no problem with earlier versions of Thunderbird and gmail.

Eh, it was user error. I had accept cookies turned off in Tbird. Set it to accept cookies and it authed okay.

Solved.

1. Set `general.useragent.compatMode.firefox` to `true`
2. Delete saved "oauth passwords" related to the account
3. Get Messages -> popup -> authenticate (one of my accounts had 2 phase auth, one not yet) -> Thunderbird automatically saves the "oauth password" (token).

In my case it was not a user error, I had this property set to `false` after a clean installation into Kubuntu. It took me several hours of my life, meh ...