Attempted to run the latest macOS update on my new iMac. After download there is the pop-up that offers to Restart and finish the install. However, on my machine selecting Restart initiated an repeating loop of requests to restart the system and asking for my login credentials. A repeating loop. But I repeat myself.
Rather than force a hard restart I logged out and logged in and then requested the system restart to complete the upgrade. That seemed to do what I expected.