oh yeah. I've once bought a $10ish one on Amazon out of curiosity.

There's the yellow composite plug, a 12V input, and a small bit of wire to be cut to rotate image 180 degrees, at the other end of a 30ft cable from the camera. The composite goes into the existing infotainment. There would be a wire from shifter to infotainment that switches the display to external composite video when the gear lever is in reverse. I think it even came with a miniature hole saw in size of the camera module.

$10 and one afternoon later, I could have upgraded a dumb car to have one, complete with auto switch to backup on reverse. No software hacking needed. It's fundamentally an extremely simple thing.

Yeah, my 2005 beater has both CarPlay and a backup camera. Cost me $40 and an hour of labor.