Sonoma 14.6.1 mailbox export issue

I simply want under Sonoma 14.6.1 to export mailboxes to an external secure disk. Select a Mailbox, right click to select Export and only the current unread emails are exported to the external disk with a very small .mbox file. Tried Command A to actually mark all emails and still only get unread emails. It used to work pre-Sonoma perfectly. Bug or is there now another way?

[Re-Titled by Moderator]