I think I found a solution for updating my newly-acquired Elite status on flights that I booked before I obtained Elite status, but will be taking later this month and next year.

Go to a previously booked future flight, click on Special Services Add Ons, don’t really add anything, run through the screens, then confirm. I think that caused something to update for me.

Only then was I able to see a free carryon option (and some free seat change options - but not the stretch ones yet because I’m only 20k Elite) when I then went back to Manage My Flight for seat/baggage purchase.

FYI, just confirming no seat/baggage changes in Manage My Flight didn’t trigger an update to give me Elite options. I had to run through the Special Services Add On first.