Startup Security Utility (Mac mini 2018) not working after Big Sur (macOS 11.1) upgrade to Catalina (10.15.7)

Hi,

I have a Mac mini 2018 running macOS 10.15.7, this has a functional admin account. Cmd + R works fine and I can boot into the Catalina Recovery OS without issue. I can also use the Startup Security Utility and authenticate access by clicking 'Enter macOS Password' to progress to the utility options.

However, when I install Big Sur (11.1) the Mac mini functions fine but when I enter the Big Sur Recovery OS I can get into the fully recovery interface by entering the admin password, however, when I enter the Startup Security Utility I get to the Authentication Needed screen but the 'Enter macOS Password' button does not work! I can click all day long to no effect. Therefore I cannot change the T2 security settings.

My original settings were no security and allow external boot.

I deleted the SSD and recovered from the internet, which fortunately recovered me back to Catalina and allowed a restore of my Time Machine backup to immediately prior to the Big Sur installation. Again under Catalina the Startup Security Utility worked fine and could be authenticated by the Admin account on the Mac mini.

I then changed the security to Full.

I subsequently upgraded again to Big Sur but the same problem occurs I cannot authenticate the Startup Security Utility because the 'Enter macOS Password' button does not accept clicks despite flashing blue when I click.

Any ideas about how to fix?

Thanks