2019 iMac won't update to Big Sur OR Monterey
I have a 2019 iMac running on Catalina. I completely forgot to upgrade to Big Sur, and would like to update it to that OR Monterey. When I go into software update in system preferences, I get a spinning wheel. When I go to manually download Big Sur from the app store, I get a "finding updates" message with the blue progress bar stuck on full, nothing else happens. HELP! thank you.
iMac 27″, macOS 10.15