My Mac is frozen on an update and won’t do anything

Press and hold the power button for 5-10 seconds until the computer turns off, then restart the machine. With any luck it should complete the update process and take you to the login screen.

The Last Security Update for High Sierra >> Download Security Update 2020-005 Post Date: Sep 24, 2020.

There have been no additional UpDates for High Sierra issued by Apple.