perhaps try the instructions here. https://thunderbirdtweaks.blogspot.com/2019/09/i-lost-my-profilemail-on-update-to.html

Thanks Matt !!! it worked!! ..... I noticed that someone posted the following on the blogspot; " I just moved the profile data from the old one to the new one it created whilst Thunderbird was closed and when I restarted it, everything was fine. For good measure I edited the profiles.ini to remove any other profile references aside from the new one. " I'd like to do the same. Where do I find the profiles.ini? Or should I just go back to the "about profiles" and delete the other profiles. Or as a third option delete them from the appdata/thunderbird/profiles directory ?

Do it all in about:profiles. editing profiles.ini is what got a lot of these folks here in the first place. It is a simple file, it is text. but I don't manually edit my own. A good rule of thumb is if there is a user interface to do something. Use it. Manual editing may work 99 times out of 100. But unless you have read the source code that updates it, you are not even aware of the checks that need to be made to ensure the change will work, let alone being in possession of the precision that a computer can bring to editing in running through a list of checks every time.

I don't bother deleting, , I tend to add profiles. disk space is cheap and having more than one allows you to try out things, including add-ons without risking you main data store and profile.

Thanks Matt ......