You may have lost nothing. Sometimes Thunderbird 'loses' info on where profile is after an update, so it then resorts to prompting for an email account to create a new profile. Start Thunderbird, ignore the email prompt, select the home tab, if menu bar isn't visible, right-click and tick menu bar. Then, click help>moretroubleshootinginformation, scroll down to 'profiles', click 'about:profiles' and your profile may appear. If so, select it and all may be as it should be.

Thanks. I actually closed Thunderbird and started it up again and that fixed the issue!

I seem to have the same problem. Except restarting didn't help. Nor rebooting. All the folders exist on disk, webmail based email for this account works fine, All the account settings are in there, the mail is there (I can search for email and find it fine), but none of the folders are visible in Thunderbird.

I've tried restarting in Trouble shooting mode, disabling all addons, nothing works.

Any help would be greatly appreciated.

Not sure if this is relevant - when I look at the error console I see these calendar related errors