There’s no external indication when someone is recording the passthrough footage on the Quest 3.
It’s a Meta device, I’m sure it’s ALWAYS recording. Whether or not the used keeps the recording is another matter.
So if the person is wearing one, just assume it’s recording and facial recognition is occurring in post.
Although it’s white LED on the front of the headset instead of the expected red. It’s seems like a dumb choice by some design team going for aesthetics over functionality. And if you’re trying to surreptitiously record people there are a million easier, less obtrusive ways to do it that don’t involve strapping a giant and expensive headset to your face.