Using the latest iPad app V10.4.4899, if you create a new message, “after typing in a recipient”, you press the Tab key which jumps down through the CC, BCC and Subject lines ok, but “won’t tab down to the message body”?
When you press the Tab key in the Subject line, it just jumps back up to the To line and goes around in a loop.
Tested on two different M1 air iPads with OS 26.4