Can you post a screen shot with the contents of your Local Folders which you will find in the Mail folder of the Thunderbird profile.

Here it is. All of my subfolders are gone.

Knowing how you did the backup may prove helpful. Can you also do a screenshot of the backup itself: the profile (if you backed up the profile), the Mail folder and the Mail\Local Folders folder. Thanks

Here it is. All of my subfolders are gone.

This is not the screen shot I had asked for since it shows the Local Folders in the folder pane. I want to have a look at the Local Folders in the folder Mail in the profile to verify whether your "Exemple.sbd" folders are accompanied by a mailbox file "Exemple" without extension. If you have created a folder "Exemple" in Local Folders (in the folder pane) und then created sub-folders in "Exemple" the presence of the file Exemple is essentiel for displaying Exemple and its sub-folders in the folder pane, even if itself contains no messages. I have seen several users "loosing" their folders and messages in Local Folders after applying so-called "Cleaning tools" which clean up every mailbox file with a 0 (zero) kB size they can find in profile...

I add a picture with the path to my Local Folders in Thunderbird profile (on a Mac). I would like to see the contents of these Local folders

I don't have that view available. When I look under C:>Program Files> there is no Thunderbird file, even though I kept Thunderbird open. I then decided to reinstall Thunderbird, and it's also running. The newly installed is V146, while the original Thunderbird is 128. So, I guess it never updated itself, which may explain why I started with problems about a week ago when my filters stopped working. And within the past couple of days it started sending "Authentication Failure" messages. This was before I tried to backup [edited email from public] @gmail.com. I'll include all the screenshots. I have a feeling that something is corrupted and I'll have to start from scratch.

I can't reproduce your view. In fact, Thunderbird was missing from C:>Program Files. So, I downloaded it again and found that the version was later than the Thunderbird I still had open. The original is V128; the one from today is V146. Apparently V128 wasn't updating even though it was set for auto updates. When I checked C:\Users\***\AppData\Roaming\Mozilla\Thunderbird all I had was a Crash Reports file. When I checked C:\Users\***\AppData\Roaming\Thunderbird\Profiles I have two, both with todays date. One has 48 items, the other only 1. I will include screenshots of all of this. Several days ago I started to experience problems with my filters not working. And since yesterday I'm getting a pop-up with "authentication failure". This has all occurred with V128. This was before I tried a backup/restore of one email account today. I suspect that V128 is corrupted in some way. If so, I have the feeling that I'm going to start over with V146. I'd like not to as I'll be loosing all of my local folders and mail. Maybe there's something else I'm not doing? Thanks.

This gets more and more confusing, there are more problems than just the disappearance of some local folders. The first of your six pictures shows the folder Profiles with two profile folders in it: the xxxxxxxx.default-release folder should contain the actual profil. But when you open this folder (second picture) I can only see the contents of a newly created virgin profile: all files and folders have an actual time stamp from today and the folder Mail is missing. That means that it is a fresh profile without accounts etc...

Now we have a rather confusing situation. The last screen shots are not reflecting what you showed in your first screen shot of the main TB window and a populated folder pane. I presume that you downloaded and installed the actuel TB version 142, then starting TB 142 which created a new virgin profile. This no longer is the same story as in post #1 .....

Reinstalling is making a small problem into a much bigger one. I suggest you, manually, go through each profile in windows file explorer, looking for the Mail folder and the Mail\Local Folders folder and do screenshots ONLY of those that appear to have content. That is files that you recognize. That will simplify this and keep from getting into the weeds.

After backing up a specific email account, and then checking the backup under local folders I only have those backup files under local folders. All of my subfolders in local folders are gone. How do I restore the original local folders? Thanks, Matt

This was before I tried a backup/restore of one email account today

I would like to understand better what you did. It may help us understand the current situation and make sure that we are defining the problem accurately.

It does not make sense that 1) you did a back-up, 2) you checked the back-up, and now 3) all your subfolders are gone. Gone from the back-up? Gone in your profile? Both? Because you also restored from the back-up that you just made?

As David asked: How did you do the back-up? And how and when did you do the restore?

Do you have other back-ups of your profile?