On iMac 21.5" late 2015, currently on El Captain.
Upgrade goes fine but hangs at "less than a minute remaining". Frustrating.
Turned off and on. It restart the install (29 minutes left) and hangs again at less than a minute.
Safe mode boot did not help: loops on the Apple logo.
HELP, PLEASE Apple!
iMac Line (2012 and Later)
After 3rd attempt, the reinstall process took place again. Then I had the "less than a minute remaining" progress, but I left home for a dinner at friends. When I came home 8 hours later, MIRACLE, the upgrade did finish successfully and I was on the login screen of Big Sur. So at the end, patience and perseverance paid off!
Safe mode did not help. It entered a kind of loop with Apple logo and progress bar at very first step, looping on and off...
If upgrading from macOS Sierra or later, your Mac needs 35.5GB of available storage to upgrade. If upgrading from an earlier release, your Mac needs up to 44.5GB of available storage.
Big Sur installation stuck at "Less than a minute remaining..."
