I completely underestimated how widespread the issue of servers not supporting TLS 1.3 is. Tests in the beta channel gave no indication.
I regret not working harder to at least make the error message better.
The error message in master has been improved, but I can't push that fix as long as I have ongoing disputes with Google (putting it out by temporarily admitting to collecting email addresses resets my spot in the queue to maybe talk to an actual person).