Cameras are now always on, to reduce the latency to taking a picture or scrubbing video feed. You’d need to wire the led to something tied to the data lines, perhaps.

Source? This seems extremely unlikely to me, running a camera all the time consumes a fair bit of energy and they don't take long to turn on. Unless that's because they're always on?

Regardless, that's a pretty strong claim. I'd love to learn more if you have a link that can back you up!

My M1 Macbook has some pretty extreme latency going from opening Photobooth black screen -> displayed image. Roughly five seconds to useable image.

  :00 Photobooth window open 
  :03 Camera LED lights up 
  :05 First image displayed

That's generally not the case. Keeping the camera on requires power and processing its video stream is resource-intensive.

Any links you could share abouy someone confirming this?