Long time TB user, monthly supporter. Have for years used a modified version of John Carlson’s “mb2md” php script to convert user’s data from mbox to maildir.
However, not everyone is comfortable running command line scripts, and there’s still a bit of manual work (editing filter paths, etc.) that needs to be done following a conversion.
As long as TB has been around, certainly some users are still on mbox.
Hopefully this process will be automated with upcoming v115.
If this is not already planned, am suggesting it be added in as a feature for the new version…