About Trailer coupling and licence plate: which statement is WRONG?
The choice (breakaway device OR auxiliary coupling) only applies up to 1,500 kg; above 1,500 kg a breakaway braking device is mandatory and an auxiliary coupling alone does not suffice.
Trailers with a breakaway braking device may NOT also have an auxiliary coupling; the two work in opposite ways (book p.231) and combining them is a defect, not extra safety.
A bike carrier mounted at the rear of the car does not need its own licence plate because it is not a real trailer.
The coupling of every trailer must always have an approval mark and be properly fastened, regardless of weight or which braking device was chosen.
Explanation
Book p.231 - the same up-to-750-kg rule applies to bike carriers that hide the car's licence plate from view. They get a white plate with the same registration as the car.