System startup utility not prompting for password - Macbook Pro 16 inch, Big Sur

I'm attempting to experiment with running operating systems, and following the "Change External Boot settings" steps from About Startup Security Utility - Apple Support

When I start "System startup utility", I see a window with the prompt "You will need to authenticate as administrator to change the boot security settings". When I click "Enter MacOS Password", nothing happens. There is nowhere for me to type my administrator password.

How do I enter my administrator password to change boot settings?

Device: 2019 Macbook Pro 16 inch (With T2 Security chip)

OS: Big Sur 11.1