Remove the passwords from Saved Passwords in Preferences/Privacy & Security, restart TB, enter a secure mail key when prompted for a password. See this page for how to create a key:

https://www.att.com/support/article/dsl-high-speed/KM1010523/

I was told to create a a mail key so I won't get an error message to enter a new password. Easier said than done. You people that know computers can probably do it with ease. Why should I be doing that anyway. For years I have had Thunderbird and all of a sudden I can't use it anymore and Thunderbird help is useless. It seems they want to lose people instead of gaining them.