Time Machine backup disk won't eject in Big Sur
My Time Machine backup won't eject in Big Sur. I looked on this forum but only found an old thread from 2015 (El Capitan). Time Machine is reporting it finished backup (eg 20 minutes ago), the hard drive doesn't seem to be writing, I have tried ejecting through Finder. but nothing happens. Disk Utility says it is not mounted and the drive is greyed out but it is still whirring and I get the usual "did not eject drive properly" if I manually disconnect. Ejecting through Disk Utility makes it start shutting down but then it automatically starts up again before I can disconnect.
It seems to be an issue for others as well - see the MacRumours forum: https://forums.macrumors.com/threads/taking-a-long-time-to-eject-time-machine-disk.2269534/
I am posting here in case others are having the same problem.