Hello again, here a couple of images where I try to explain to you how it works:

If you can see well, between the TX- and TX+, there is a 2V coming from the rs485 module, it is a "problem" because when the camera responds at the query on the same pair of wire, the signal from the camera is cut out by this 2v (lowered to a volt difference about 200mv).

I'll figure something out for next time!

See you next time !