After update, Thunderbird can't find Trash or Sent folders
On September 5, Thunderbird updated to 155.0 (20260828141248) (on Windows 11 10.0.26200). I use IMAP.
Since then, when I try to delete a message, I get an error: The current operation on ‘Inbox’ did not succeed. The mail server for account <email address> responded [TRYCREATE] Mailbox doesn’t exist: INBOX/Trash (0.001 + 0.000 secs)
But in Settings, "When I delete a message: Move it to this folder: Trash" is set. Not Inbox/Trash or INBOX.Trash, which also exist, but Trash at the same level as Inbox. I logged into webmail for this account, and there's definitely a folder for Trash. All deleted messages prior to the update are still there. If I delete a message in web mail, it is moved to the Trash folder.
The same is true of the Sent folder. In Settings, "When sending messages, automatically: Place a copy in: "Sent" Folder on: <account name>."
It looks to me like Thunderbird is doing something different from what the Settings say, and definitely something different than what it did before the update.
Suggestions?