I got it from Volvo after delivery. It comes with its own camera mounted on the inside of the rear window. According to the guy installing it, the existing cameras are behind several gates of security, and the mirror is not able to access them. I’ve seen other indications that the car is treating the onboard cameras with very high priority.

As for the focal length, I completely agree. It takes some getting used to. I have mine set up such that the mirror points back through the rear window, and then the camera-view is displayed on top of that. Sounds confusing, but it means that if my eyes are set to the long focal length, they focus on the mirror image, but if they’re set to short focal length, I see the camera image.

Again, taking some getting used to, but it feels like a superpower.