List of users always displayed at startup instead of username & password, regardless of System Preferences setting

I am having a very strange issue and found this post (https://discussions.apple.com/thread/6867900) describing the same issue dating back to 2015. It appears that multiple people had the same issue but there was never any resolution. It is currently 2021 and I'm on a 2019 MBP16. I noticed this issue some time ago but didn't pay much attention to it. Recently I upgraded to Big Sur and was curious to see whether the upgrade would fix it. Alas it did not.

The issue is that when starting up my computer, I am always presented with a list of users rather than username and password fields. This despite having selected "username and password" in the Login Options area of the Users and Groups system preference. I have tried this multiple times using multiple user accounts, and nothing changes. I do have filevault encryption turned on, and I note that one user in the original thread suggests that the startup screen is actually a file vault unlock screen not the login screen, and the appearance of this screen can't be altered. But every other mac I've used follows the System Preference setting correctly, so this is clearly not correct. Is anyone else having the same issue? Is it possible there is a corrupt preference somewhere, and if so how where to I find it?