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.