More information may help. is this an IMAP account or POP? Would you please create a screenshot of the associated folder for the account in the profile folder? That may prove useful. thank you

It's an IMAP account. It seems like I've found the solution to my problem. I have an extensive folder structure for my emails, see the attached image which is only a small part of it. I have always installed Thunderbird by default so far and then the profile directory is created relatively far down in the folder structure under "users". Now I tried to move the profile directory much higher up in the directory structure and then got a significantly shorter folder structure and then all the folders became visible. The problem occurred in connection with the latest update so it seems like the latest version can't handle as long search paths as the previous version did.

The image you supplied is not an imap mail account, it's the 'Local Folders' special account.

re :I have always installed Thunderbird by default so far and then the profile directory is created relatively far down in the folder structure under "users".

If you downloaded Thunderbird from the official webpage: https://www.thunderbird.net/en-US/thunderbird/all/

Then the profile would be in a relatively short location: C:Users/username/Appdata/Roaming/Thunderbird/Profiles/profilename

It would be very different location and a much longer location if you installed thunderbird using the Windows App store. C:\Users\username\AppData\Local\packages\MozillaThunderbird.MZLA_h5892qc0xkpca\LocalCache\Roaming\Thunderbird\Profiles\profilename

Windows OS may have a limit set up - 260 character limit. You could try getting it extended. I found some info on the microsoft website using google search. https://learn.microsoft.com/en-us/answers/questions/1434888/long-path-not-working-and-i-am-unable-to-rename-th https://learn.microsoft.com/en-us/windows/win32/fileio/maximum-file-path-limitation?tabs=registry

To enable long path support in Windows 11, open the Registry Editor, navigate to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\FileSystem, find the 'LongPathsEnabled' -double click on it to edit the DWord value, and change its data to 1.

I have always done my installations from the official website and installed them with the default path C:Users/username/Appdata/Roaming/Thunderbird/Profiles/profilename. And it has worked fine until the last update when I had problems with missing folders and emails. I then moved my profile folder to C:Mail/profilename. That solved my problem and now all folders and emails are visible again.