What happens when you start in troubleshoot mode https://support.mozilla.org/en-US/kb/troubleshoot-mode-thunderbird ?

Troubleshoot mode won't do anything at all as you can see in this screenshot.

The only thing I managed to do was display the folders: Favorite folders and Recent folders. Even though I have all the folder modes options checked, only Favorite folders and Recent folders are functional. All folders are unchecked by themselves when I go to the menu again.

When I go to the Folder Mode menu again, only Favorite Folders and Recent Folders remain checked. I would need to still have All Folders displayed.

I am very disappointed. I expected more interest in this bug from the developers. I am a long time user of Thunderbird. I have brought many people to use this program. Well, this disappointed me a lot.

115.3.0 has some fixes in this area. You can install from https://archive.mozilla.org/pub/thunderbird/candidates/115.3.0-candidates/build1/win64/en-US/Thunderbird%20Setup%20115.3.0.exe - let it install in the default location. Please post your results.

I already have version 115.3.0 installed via update. But I downloaded the version from the link you provided. Unfortunately, I still can't see (turn on) All Folders. When I check All Folders it doesn't do anything but add a pipe there. But when I go back to that menu again, it's not checked. The program does not respond to it at all. The only change is that I now have Thunderbird in English. It is installed in "C:\Program Files (x86)\Mozilla Thunderbird".

What helped me was to remove the diacritics in the mail.server name (RSS kanály) in the prefs.js file. See https://bugzilla.mozilla.org/show_bug.cgi?id=1857824