Why are you required to stop here?

In this situation, you are required to stop because a cyclist is approaching on the priority road from the left. The intersection is regulated by a "Yield" sign (Vorfahrt gewähren), which means you must give way to all vehicles coming from the priority road before entering. According to German road rules, especially at yield-controlled intersections, cross-traffic on the priority road—including cyclists—has the right of way. You only need to stop if someone on the priority road would be affected by you entering.

In this case, the cyclist is the one you must yield to, so stopping is correct. Neither the green car (which is parked) nor the pedestrian cause you to stop in this context. Always look for moving traffic on the priority road, not parked vehicles or pedestrians who are not crossing your path, when deciding whether to stop at a yield-controlled intersection.