We’ve seen several reports regarding failed upgrades from macOS 10.14.6 Mojave to macOS Big Sur. The symptoms are:
- After reboot you get the apple logo with progress bar stuck, with it never completing the upgrade
- Previous user account gone (files locally available under /Users)
- Can successfully boot safe mode.
It’s recommended to upgrade to macOS 10.15 Catalina first as an interim step. You can then safely upgrade to Big Sur.
The download link for macOS 10.15 Catalina can be found on this page: https://support.apple.com/en-us/HT211683
You can also upgrade via Jamf.
If your computer is in an inoperable state, you may need to do a clean installation of macOS. If you need to recover files from your computer first, please consult your support person or restore from a backup.