iMac: can't upgrade, stuck on "Finding Update"

Been trying and trying, but my computer refuses to find any macOS updates, so I'm stuck on Catalina and need to have at least Monterey running for my new job (can't upgrade my MS Office apps because they require Monterey or higher).

I've tried safe mode, tried to d/l the upgrades from 3rd party links, tried everything I can think of and find online. The farthest I get is System Update dialog box with the blue progress bar pulsing under "Finding Update". I've left it overnight with no result. This computer is only two years old and has plenty of storage and RAM to run the update install. W. T. F.