I've just fitted a dashcam with reversing capability, wired to the fusebox and the reversing power in the boot. It works well: not as large a screen as the sole purpose dashcams, but big enough, with guidelines and a STOP line. I checked it out this morning by not backing into our front porch. Even with a new plastic screen (you should have heard the bang when the old one split from side to side!) it is very helpful.
I got mine and the wiring kit from Temu for a ridiculously low price. I've seen better images, but it's not bad. Example
HERE, after the static photos.