Problem:

The screen flickers during face unlock in dimly lit conditions.

Reply:

The face image collected by the camera could be of poor quality in a dimly lit environment. To compensate the lack of light for the face and thereby improve the speed and accuracy of facial recognition, the screen auto-increases brightness (which seems like the screen flickers) under dimly lit environments. If the ambient light is low, you can use your fingerprint to unlock the screen.