The fingerprint reader will periodically ask for the PIN or password, since the biometric is considered less secure. I don't think I could face the hassle of having to do 2 things just to use the phone.
My one complaint about the fingerprint reader on my s21 is the way they handle this periodic verification. With my old Pixel 2 when it wanted this the screen would light up when you pressed the fingerprint reader and tell you that the PIN was required. With my s21 nothing happens at all, you just end up pressing a few times until you realise that it's not that you are missing the sensor but that it must want the PIN, then wake the screen up manually so you can enter it (the message is there when you wake the screen, but by then it's useless as you've already figured out why it isn't responding). It's a stupid choice which makes the intermittent verification more annoying than it needs to be, and is something that the Pixel did much better. I don't know whether it behaves better if you use the ambient display, but if that's the answer then it's a different stupid choice because if a feature is optional you shouldn't assume everyone will use it.
