My guess is that the order of operations is important somehow. I’ve experienced a similar situation with a brand new setup, but as I recall, macOS never asked for full disk access.
I managed to get things going, but perhaps the DT UI might be redesigned in such a way users are guided through the appropriate steps. That way DT can get feedback from the user whether all steps were taking correctly, as I understand macOS does not allow third party software like DT to request the status of certain settings like full disk access.
I’ve written out what happened and my suggestion here:
But of course, if an IMAP connection is integrated some day (who knows), all of this will likely be much easier
