It’s always dangerous to jump to conclusions when you don’t know what is going on. I have no problems with notes, never did. Neither on Big Sur, before, or on Monterey. You said you just upgraded? Is there any kind of indexing or synching going on? Have you given the upgrade awhile to finish indexing?
You say you have a lot of notes, syncing to iCloud? Shared notes, embedded stuff?
I upgraded to Monterey when I got new m1, it is fantastic. No problems at all. Can say the same with Big Sur on my old computer. And I’m on developer betas, so my builds should be less stable, not more
If you had a lot of crud because you haven’t done a clean install for awhile, do it. I had a bad framework once, crashed safari. Clean install later. Everything was great