Hey Ruby! As others have noted, yes you can but your reason to roll back to 20H2 (worried about Windows 11) really has nothing to do with the fact you are using 21H1. 21H1 is still Windows 10. I recommend you stay where you are and make a good image of 21H1. Then, once W11 rolls out, give it a good, honest and fair try. Give it time to get used to the new features. If you don't like W11 (or whatever they end up calling it), you can roll back to 21H1.
That said, because of the advances in security (that attempt to keep up and stay just ahead of the advances made by the badguys), it is never a good idea to stick with old, outdated, and soon to be unsupported (thus insecure) versions of Windows.
At this point, there is no reason to believe the upgrade from W10 to W11 will be a disaster. Contrary to all the bad hype from the IT press and MS haters that always accompanies these upgrades, the skies don't come crashing down and the upgrades happen smoothly for the vast majority of users. And out of the few with problems, they tend to be easily resolved.