My understanding is that the Infotainment system receives a signal that the car has been put into reverse either via a CAN Bus message or from a voltage via one of the BCM pins, and not from the Rear View Camera.
If you think about it logically, the Infotainment system will switch on the OPS when the car is put into reverse even without a camera fitted, so it can't be the camera that notifies the Infotainment system that the car has been put into reverse. The trigger wire from the reversing light circuit to the camera is simply used to turn on (power up) the camera itself. The two wires that go from the RVC to the quadlock connector on the Infotainment control unit only carry a video signal and nothing more.
So your Infotainment system will be switching to the camera display mode when you put the car into reverse based on the
coding you've done, but it won't be receiving any video signal from the camera on the 2 quadlock wires due to the camera not being powered up so that would explain the blank screen.
Below is the wiring diagram for the inner tail lights on the boot lid that contain the reversing light and fog lamp. The reason for the wiring diagram showing two different sets of wires going from the BCM (J519) to the reversing bulb and the fog lamp bulb is because the two lights are swapped over on LHD and RHD cars with the fog lamp always being on the offside of the car.
I've also included another wiring diagram that shows the RVC wiring on a
Leon Mk3. This isn't an official diagram because one doesn't seem to exist, but it's one I've created myself in the same style as other VAG wiring diagrams and it's been compiled from wiring information I found for the same type of RVC that's installed on other VAG cars. I'm fairly confident that this custom schematic is an accurate RVC wiring diagram for the
Mk3 Leon. This also shows two wires going from the BCM to the "power on" wire of the RVC for the same reason that on a LHD car the reversing light voltage comes from BCM pin
T73a/64, and on a RHD car the reversing light voltage comes from BCM pin
T73c/11.