FWIW, when I originally experimented with wildcard aliases I created, for example, the alias
xyz@sent.com and then a sending identity *@xyz.sent.com. Selecting that from the compose sender popup produces an editable From (and I assume should still work for
everyone). But I gave up on these kind of wildcard sending identities because of some "quirks" I didn't like.
Quirk 1: If you have a number of sending identities in the sender compose popup then whatever is shown as the selection in the popup would supply the name part of an email address to replace the * when you selected the wildcard alias. While you always would have to edit the From anyhow I would have preferred it just left the * in the initial From address and not show an unassociated name.
Quirk 2 (most annoying): If the recipient replies to whatever you used, and
you want to reply to that, the From in the reply compose doesn't show the sent address you used so you
always must edit the From: in your reply to their reply. This is the inconvenient. Why isn't the default reply supplied from the To: of the reply you are trying to reply to?