Admin authentication not working on Big Sur Anything that I am trying to do that requires admin user access is failing. Whether it be moving an app to the trash or making a change to settings (app settings or system settings) it isn't working. The normal window pops up that has me enter my password but when I hit return or select the OK box on the auth window everything just greys out and nothing happens. If I'm deleting an app another box pops up showing progress but it just hangs. There appears to be no way to close the Enter your password to allow this. windows so I have several hanging on my desktop.
Has anyone seen this yet/know why its happening?
I would make a second admin account, maybe something simple and insecure like me/me and then try to see if the problem is your account or if you can open it with the “me” admin.

First test when your old account is logged in, when the admin prompt arrives, change your user name to me and use the “me” password.
Then log out as you, and see if me can unlock their account.

This sort of thing is hard to guess from a far, but easy to corner and once you have a cornered you’ll know where the problem lies. Everything you mention is explained by a corrupt user preferences (or worse, failing filesystem) so be sure you back up all your critical files immediately and get a Time Machine or whole system backup sooner rather than later.