On the Windows side you can find Windows Hello certified third party cameras with the necessary IR and depth sensors. (I've seen Intel and Logitech options in stores.) Since the death of the Kinect the cost has generally gone way back up as it is a niche of a niche just to support easier logins and few applications anymore are using the IR/depth sensors as much (though even this far past the Kinect, Windows itself has additional eye tracking/attention tracking features these days than it ever had before for accessibility reasons).

Surely Apple could release a FaceID-compatible USB webcam if they wished. It's probably less likely for them to FaceID certify third party hardware, though.

(That said, I think Apple's other excuse for not supporting FaceID on more hardware is it uses the ML capabilities of some of their mobile A* chipsets. Maybe another thing they might claim can only be done with M1+ macOS.)