Why I have been locked out of making changes to the system preferences since the Big Sur update?

Since I updated to "macOS Big Sur" a couple of days ago I can't make any changes to my security settings. If I click the lock it requires my login password which I obviously know otherwise I wouldn't be able to login to my mac. However, when I type my password required to make changes to things in system settings (e.g. Security and privacy) it acts as though I have inputted the wrong password.

As a result, I tried changing the system password slightly. Again, I could login just fine but it made no difference in changing the system preferences. I still can't access it and it must be triggered by this update as it worked fine before the update. How can I remove this update when the stupid system won't recognise my login password?