The last few times flying back from EU through CDG, security funnels all US passports (and Brazil and South Korea maybe?) through a face ID gate for passport control. There was no signage communicating an opt out policy, although it’s my understanding that opting out is allowed. Flight connections have always been fairly tight though, so I didn’t press the issue unfortunately, and was unsure of the rules at the time. I opt out domestically, although it seems this is so infrequent they just have the camera scanner running as soon as you walk up, before you can even get close enough to request normal screening.