You intend to turn left. Are you obliged to yield the right-of-way to all vehicles at the junction?

Why?

The B-20 stop sign requires you to stop and give way to traffic on the priority road, including the motorcyclist approaching from your right. Because you are turning left, you must also let oncoming vehicles travelling straight ahead pass first. In this situation, that means giving way to all those vehicles.

§ 21 ust. 1 rozporządzenia w sprawie znaków i sygnałów drogowych; art. 25 ust. 1 Prawa o ruchu drogowym