Did you accidentally hide your Local Folders via the "3-points" menu > Hide Local Folders"? (image 1) What is selected in View > Folders ... ? (image 2) Did you accidentally rename you Local Folders in Account Settings > Local Folders > Account name? (image 3)

Thanks for looking into this. 1. Hide Local Folders is not ticked. 2. Selections in View are exactly as your image. Only items ticked are Folder Pane Header, and (greyed out) All Folders. 3. I can't think that I did. I was busy all day uploading Windows 11 and didn't do anything with TB excepy download new messages and maybe send. Local directory is C:\Users\bob\Desktop\Local Folders, and Account Name is Local Folders. Looking at folders again now, The Sent folder also disappeared. I have just sent a test message and the folder has reappeared but only holding that one message. Search shows I still have another 72 sent messages in the system, but not in the folder. As I say, the Local folders are all gone, except for Deleted and Outbox (both showing empty).

Your Local Folders are not located in the Thunderbird profile but on your Desktop. Maybe this is the cause of them not being displayed in Thunderbird in the folder pane. In your Thunderbird open the Account Settings tab, select Local Folders in the left pane (accounts), go to Message storage in the right pane > Local Directory and take a screen shot of the actual path to your Local Folders (see image).

If the path to Local Folders doesn't lead to C:\Users\bob\Desktop\Local Folders, click on "Browse...", navigate to your Desktop, select "Local Folders" and click "Open". Thunderbird will prompt you to restart the app, after which you should see your missing your old Local Folders

Desktop\Local Folders is empty, and no prompt from TB.

Can you go to C:\Users\bob\AppData\Roaming\Thunderbird\Profiles\xxxxxxxx.default-release\Mail\Local Folders\ and make a screen shot with the contents of "Local Folders"?

From 1st image you'll see I only have -release for an old 2020 profile. Second is of that profile's local folders contents. 3rd image is Local Folders of what I understand to be the current profile.

I have my most important emails also on my laptop, which has most of the same local folders, on its Desktop>Local Folders. Is it a safe idea to import from there to the PC? Perhaps as a last resort?

Thanks for the new images. Obviously the profile 9ujgg8q.default is your current profile. When I give it a closer look, the Local Folders contain an Inbox file with a 11.6 MB size, a Sent file with 1 kB (shouldn't be more than one message) and a Trash file which could contain several messages. It is a bit surprising to see the Inbox ans Sent files in the Local Folders, but maybe you have a POP account for which you chose the "Global Inbox (Local Folders)" via the "Advanced Account Settings" in Account Settings > Server Settings > Message Storage... So which folders in the Local Folders are you looking for? I don't know since this isn't my Thunderbird installation, so actually I am unable to tell where to look for your hypothetically missing folders. Your screen shots dont tell where they are.

There is one thing you didn't show yet: which is the contents of the Local Folders on your Desktop?

I have POP3 if I recall correctly. The advanced settings for Message Storage is set to "Inbox for this Account" Struggling to save screenshots this morning. In the meantime I can list the contents of Desktop>Local Folders. msgFilterRules (DAT 0kb), Trash (File 0kb), Trash.msf (MSF File 2kb), Unsent Messages (File 0kb), and Unsent Messages.msf (MSF File 2kb).

There are several local folders and sub folders, such as 1.Rob Saved Items, Car, Highfield, Planning, Properties and so on. Using Search for individual messages reveals which of the folders the messages are in, so the folders must still be here (somewhere).

I'll keep working on the screenshots.