Checking for Updates Just Churns & Churns

I updated to Big Sur on my 27" 2017 Retina 5K yesterday and want to update to Monterey. When I click on the Apple icon (upper left corner) and click on Software Updates, the "Checking for updates" just churns and churns for hours.

Everything else on my iMac is working fine.

Why does the "Checking for updates" churn? How to fix?