Go to Settings > Face ID & Passcode > Set Up Face ID. When trying to setup Face ID on the iPhone, we get the message 'move iPhone a little lower/higher'.

Start the Camera app and select Portrait in the bottom bar. Switch to the front camera. When the camera detects a person's face, the name of the lighting effect ‘Natural Light’ stays the same. The pop-up notification keeps saying ‘Move farther away’.

Normally, when Portrait mode is ready, the name of the lighting effect ‘Natural Light’ should turn yellow.

Judging by this, the dot projector or relevant circuits of the dot projector might have malfunctioned.