I installed an aftermarket multimedia system with a parking camera on my Octavia, now I have a problem that the camera only turns on when the engine is not running,

Which Radio? Which Camera,?

some Chinese one from aliexpress, everything works but the camera only works until I start the engine

I read that the problem can be solved by installing a relay, because the plus from the camera is connected to the plus of the reversing lights.

and now I'm wondering where I could find the plus in the rear of the vehicle, I found it in the cigarette lighter but there is a constant 12v, it doesn't go out and it doesn't go away even when I lock the car, I wouldn't want to connect to that place,

I personally plugged it on the rear wiper with a hardwire kit.