I tried "Better"bird for around a month, a year or so ago. Until I hit a bug and submitted a bug report and got this reply:

That’s best reported as a Thunderbird issue with exact steps to reproduce.

and later this:

As a first step, we suggest to install the current ESR 91 version of Thunderbird in parallel and see whether the issue exists there.

I personally don’t see what’s the point of using an email client, if it refers to another email client for submission of some bugs, or if it asks you to install another email client to solve them. I told them and they explained that they’re a small team and that

BB is a TB downstream project (fork) and we cannot possibly fix all 14.000 upstream issues.

The turning-point for me was that they simply closed my bug report and, when I told them that that was a let-down, they said:

Users like yourself, who refuse to cooperate or support the project via a donation, are a total let-down indeed, especially if they feel entitled to get a fix.

which was unfair because I do recurring donations to all software I use regularly. But OK, I can simply donate directly to Thunderbird and use that directly.

So I went back to Thunderbird and have been using it without problems since then; they fixed that and other bugs in the meantime. Thunderbird supports all major forms of authentication from what I’ve seen, so I use it for my work account and other free accounts, all in one.