Mac won't recognize password for software update

Hi, and thank you again. I was not able to clear enough space for a full install, but happily, I was able to find a fix.

I decided to play around a bit in an older user account, a standard (non-admin) one, and I noticed that to do certain tasks I had to enter my admin name and password (which always worked).

I reasoned that perhaps it would let me install the BIg Sur update by entering the admin password from OUTSIDE the admin account; in other words, perhaps the bug wouldn't hinder me that way.

From the old standard account, unlike the "Test User" account I built on the phone with Apple the other day (which did not show any updates available), the Big Sur 11.3 update showed as available.

To my surprise, it did not even require an admin password. (I do not understand this — I have to have an admin password to make the simplest of changes but not to update the OS?) Anyway, when I entered the password for the standard account, which is likely the first account on the history of my Mac migrations (my brain has lost track, even if my Macs have not), Big Sur did in fact update and is now at 11.3.1.

I hope this helps someone else in the future. Thank you for taking the time to reply and help open my brain to solutions that led to finding a working one.

Hi, Claire, thank you.

Yes, I'm running as an admin... everything is the same as it was under my ex-husband's name but now with mine. These are the steps I followed in doing so: https://support.apple.com/en-us/HT201548

I called Apple yesterday and the agent was unable to resolve the issue. We tried to do a full install of Big Sur in recovery (? the mode where you hold for 10 seconds and select options) but it said my 32 available GB are not enough for that (I've deleted everything possible in an attempt to make room — I'm running this pretty clean, I think). She also advised me to try making an admin test user, but oddly, no suggested update offered Big Sur 11.3 as an option as it does for my regular admin account. So we were unable to attempt an update with Test User.

For now I have turned off "Keep my Mac updated automatically." It's not hindering my work for now but I'm terrified of the issue not getting resolved and having problems down the road.

The Mac wasn't used but it was a certified refurb from Best Buy, if that has any bearing. Shoulda spent the extra $30 for a brand spanking, heh.

Hi, thank you again. Yes, the agent also had me attempt the update in safe mode, but I just did so again so I could be sure it wasn't working and report back. The only difference is that it downloads the updates again, but when it prompts me to restart and I attempt to do so, it asks for the password and won't accept it. There is a video of someone with this same issue at https://www.youtube.com/watch?v=kaquqIn5RKM — he resolves it with a full install of Big Sur, but as I mentioned, my machine won't let me do so. (At the moment it's showing 43 GB available in "About.")