Polarized sunglasses block the phone's sensors, so it can't confirm you're actually looking at the screen—That someone isn't trying to unlock it e.g. while you'

Polarized sunglasses block the phone's sensors, so it can't confirm you're actually looking at the screen—That someone isn't trying to unlock it e.g. while you're asleep. If you turn off "Require Attention for Face ID" in Face ID settings it'll work with sunglasses.