My company email is Office365 and I’ve been using it through Thunderbird for years with no (serious) problems.
I haven’t changed any settings or anything, but yesterday I opened Thunderbird on my work computer, and all the folders disappeared except Inbox and Deleted Items.
To see if it was just that computer, I tried on a home computer and the same thing happened. Both of those are running TB 52.9.1 (to use the AttachmentExtractor addon). That machine also has Gmail IMAP which has no such problems.
My main home computer is running TB 78.10.2, so I thought maybe it was a version thing, and I backed up all my ImapMail folder and then ran that, and again all folders except Inbox and Deleted Items disappeared.
The only thing in the error console is 6 instances of NS_ERROR_FILE_UNRECOGNIZED_PATH … nsIXPCComponents_Utils.readUTF8URI
If I click Subscribe… it shows all the folders as unsubscribed, but if I click Subscribe on them, nothing happens.
All the folders still exist on https://outlook.office.com/
If I Subscribe to a folder, and then restart Thunderbird, the folder appears for a second and then disappears. There are no errors in the error console with timestamps at the moment that it disappears.