LOL. I FEEL like one lucky woman! Since my last message, I checked for updates yet again on my old desktop (which I had also done the registry edit for, to get 21h2) and lo and behold, there it was starting to download Windows 10 21h2 -- even though an hr before it had told me I was up to date. All went like clockwork, hopping directly from 20H2 to 21h2. So now both of my computers are set.
On the Surface Pro, there is just the note in the right margin telling me "This PC can run Windows 11, Great news—your PC meets the minimum system requirements for Windows 11. Specific timing for when it will be offered can vary as we get it ready for you." and a link where I can "learn more about Windows 11" -- same as it has been ever since I did the registry edit about a month ago. But nothing intrusive, nothing asking me to do anything about Windows 11. So at some point in the future I may have to choose "stay with Windows 10" vs. take Windows 11. Having made the wrong choice the last time (because I was given the choice and did not realize what a big, unwanted change Windows 11 was) I will know this time to decline if it is offered. But my understanding is that the 21h2 version of 10 was offered specifically as an alternative to Windows 11 for those who didn't want it or whose computers could not run it. And I think that now that Windows 10 21h2 is my target version and is what I have, I would have to actively override that to get Windows 11.
On the old desktop, that same right margin area informs me that my computer cannot run Windows 11. So I know it will not ever come up there as an option.
Hope this helps.