this problem has been occurring since Thunderbird started out, but because particularly prevalent in V68 with a policy change. So all the information you found is probably relevant and accurate. This is mine.

https://thunderbirdtweaks.blogspot.com/2019/09/i-lost-my-profilemail-on-update-to.html

Thanks, Matt. I tried to use your approach, but it applies to an earlier version of TBird, and it went down a blind alley for release 91.4.1. I'd be grateful for any other ideas you might have. Dave Engels

Well you will have to explain why it applies to an earlier version, because I do not understand what that is meant to mean. Same commands in v91 as V68, same menu, same screens displayed, same text in the dialogs.

Hi Matt Sorry to be late getting back to you. My wife got sick ( not covid thankfully) and I've been busy taking care of her. But here's where I got stuck using your method to get my folders back. I downloaded your msg about 'I lost my profile/mail on update of Thunderbird' and very carefully went through it step by step. I had only one profile before. When I clicked on Create a new profile button, the 'welcome to the create profile wizard' opened. I clicked 'Next' as instructed, and changed the name from 'default user' to 'old profile'. When I clicked the 'choose profile button, only one name appeared in the 'Name" column, which was the old profile name. The instructions said there should be one more profile listed than is shown in the about:profiles page. But there was not a new profile, just the 'default user' profile but with the 'old profile' name. There were no other profiles displayed. I tried several times, trying to be very careful not to miss a step, but always got the same result. So I was stuck there. I hope you can help. My old folders had a LOT of very important information that I badly need and I will be very grateful to you if you can help me get them back. Also, all my mailing lists disappeared. The 'addresses' are all there, but the various sublists are gone. Thank you very much for your help. Standing by Dave Engels

Please provide info as we need to see what is actually stored in various profile folders and files.

In Thunderbird

• Menu app icon > Help > More Troubleshooting Information
• Under 'Application Basics' - half way is 'Profile Folder' - click on 'Open Folder'

A new window opens showing contents of 'profile name' folder

Make sure from now on you have the View set to show details and also make sure all images display the directory information as well, so we are certain which folder you are viewing.

• Go up the directory to the 'Profiles' folder to see list of 'profile name' folders
• Post an image showing contents of the 'Profiles' folder.

• Go up directory to the 'Thunderbird' folder.
• You will see a 'profiles.ini' file - open the 'profiles.ini' file using a text editor like Notepad.
• Post image showing contents of the 'profiles.ini' file.

Now we return to the 'profile name' folder

• click on 'Profiles' folder and then click on the 'profile name' folder.

If you used POP mail account:

• click on 'Mail' folder to see contents.
• Post an image showing all the contents.

If the missing folders were in a POP mail account:

• click on POP mail account name folder to see contents.

If missing folders were in the 'Local Folders' mail account:

• click on 'Local Folders' folder to see contents.

• Make window as big as possible so it displays the maximum amount of file names.
• Post image showing contents. You may need to post more than one image if scrollbar needs to be moved to show all of them.

Tell us the names of the missing folders.

If unsure how to create an image - info here:

• https://support.mozilla.org/en-US/kb/how-to-make-screenshots#w_create-a-screenshot-on-windows