Did you upgrade directly from 38 to 102? That may be part of your problem, as Thunderbird does 'housekeeping' at the beginning of each series. The generally recommended upgrade path is to go via first release of each series, e.g., 45.0.1, 52.0.1, etc., up to 102.

Thank you for the suggestion. Let me see if I understand this correctly. In order for passwords to work in Thunderbird, I should uninstall the version I have, then research how many "series" there are, then download these old versions, then upgrade progressively to the latest version. And maybe this will work? Note that I have already upgraded, so there is no way to tell what remains of the original versions or what files are causing the problem (I already deleted all the common culprits that are recommended to eliminate). I realize this is an open source software, built on the backs of volunteers, but this method seems like a sure-fire way to eliminate old users. There must be a simpler way to use passwords.

Any other suggestions?

I agree it is cumbersome, and only works if you still have the original profile. Over the years, Thunderbird makes changes and has code in place during the early stages of a release. By not keeping up, you can end up with a cumbersome upgrade approach. Depending on how many accounts you have, installing fresh might be a good option. But there are some excellent technical experts on this forum and if one of them sees this thread, they may have other options.

Thanks David. I do have 54 email accounts currently, and maybe 600,000 messages; with the sorting rules, starting over is a little tedious. Looks like I will have to do this one way or another. Not being a pro or anything, I am thinking that something in this version is linking to something in an old version, and that must be the problem. The other 100 threads on this subject suggested to delete 4 or 5 files (pkes11.txt, cert9.db, kg4.db, session.json), plus all older derivatives; in addition to reset the master /principle password; in addition to install the new version of the software. Obviously none of these worked. I suppose if I read a couple million lines of the code I could figure this out. Just hoping I get lucky and someone knows how to make passwords work. I am not even sure it is because I upgraded - all I actually know is that it does not work. Again, thank you for the suggestion.

If you have a secmod.db in the profile, delete it, as it sometimes blocks normal password operations.

https://support.mozilla.org/nl/questions/1373145

Solved! Delete secmod.db from Thunderbird files, and now a master password can be entered, and it remains. All else follows. Thank you sfhowes...).