The proximity sensor was removed in the backer versions of the headset. This doesn’t cause too many issues as they can simply use the lighthouse tracking to detect if the headset is moving. If it doesn’t detect significant movement for a certain time frame, it’ll put the headset into standby mode.
However, this does cause issues in situations when you aren’t moving your head very much. An example would be watching a movie. If you don’t move your head enough, then the headset will go into standby mode. This could be avoided by utilizing the eye tracking module to detect if someone is wearing the headset. If the headset is tracking someone’s eyes, then obviously someone is wearing it and there is no need to go into standby mode.