Used Windows Assistant to install the update on my 1-year-old laptop. Step 3 (Install) completed and gave me the option to restart, which I did.
Restart stalled, I waited 20-25 minutes and no response. Pressed power button to attempt to restart the laptop, it went into some strange state, and I could not get the laptop to restart. Screen was black.
I figured it was "bricked" from the update and closed the lid.
Fast forward 12 hours later: pressed power button on laptop and the update continued to complete.
Laptop appears to be running fine, time will tell. Only problem I have is the Cumulative Update KB5017321 has failed 3 times.
This is the longest and most concerning update I've received in the 33 years I've used Windows.