I know this is old, but wanted to come back and thank you
@unibility !
I have been trying for three weeks to add my Pro Display XDR to my AppleCare One plan and no one from Apple could figure out why it wasn't showing up in my list of devices to add to the plan. I opened several cases with Apple and they gave me at least half a dozen reasons why it wasn't working, and I did exactly what they claimed to be as the solution only to see it continue to fail. When I read your post, I updated to the latest version of Sequoia and it immediately showed up in the list to add. For the life of me I cannot imagine why none of the Apple engineers suggested this. Amazing fail by Apple!!!