I'm a PC, not a Mac, however... this is what I did to fix this issue and get the Setup Assistant to run, allowing the creation of a new admin account. You can skip to the instructions below if you want, but here are the details of how this happened. My wife tried to update her laptop to Big Sur, and during the process it froze on a black screen with an Apple logo and a progress bar that had moved not at all by morning. I restarted it when I woke up, and it seemed to be stuck on the same screen. I went to work. When I spoke to my wife next she was using it and said it had gone a bit further. Later on in the afternoon, she said it was working, however her account had lost admin rights. There was no other account on the laptop. Using recovery console displayed the "No users available for authorization" message. Booting into Single User Mode didn't work, at first. It took some time to figure out the right instructions. All instructions I could find on the internet said to delete the file .AppleSetupDone, but the directions on how to get to this file did not work on her laptop. First, this is what I was shown, which is also different from other posts I've seen (a lot has been omitted for brevity): To mount the root device as read-write: $ /sbin/mount -uw / To mount the data partition on an SEP-enabled device: $ /sbin/mount -P 1 $ /usr/libexec/init_data_protection $ /sbin/mount -P 2 On all other devices: $ /sbin/mount -vat nonfs To boot the system: $ exit I don't know what kind of system my wife has, but I kept trying the first mount option, which didn't work - I believe I was given an access denied message. So I finally used the second mount option(s) for SEP-enabled devices, the first and last commands of which worked. The middle command didn't work (it also returned an error message), but it didn't seem to make a difference. Now however, is when I needed to use some of my limited knowledge of linux. I had to find this famed .AppleSetupDone file. I didn't take notes while I did it, but I believe the path was as follows: /Volumes/”Macintosh HD”/var/db/.AppleSetupDone I used a combination of the following commands to change folders, list folder contents to ensure the current folder had the next folder I was looking for, and displaying the current folder name: cd _foldername_ pwd ls -l When I was in the db folder I used "ls -l | more" to pause the listing after a full screen. Press q to stop the listing when the colon appears in the bottom left. When in the correct folder, type rm .AppleSetupDone to delete the file, then restart. Note that you should also be able to do everything in one line, if the path is correct. rm /Volumes/"Macintosh HD"/var/db/.AppleSetupDone