For the last few months or even a year my macOS updates have stalled on the Apple screen with just a bit of progress bar. Somehow I discovered that if I first ejected my external hard drives (an SSD for my Photoslibrary, a hard drive for Time Machine backups, and another for Carbon Copy Clone backups) everything goes smoothly.
This was happening with my 2016 15” MacBook Pro and I was chalking it up to old age, but now it just happened with my new M1 iMac. Anyone else had this experience? Any insights or solutions?