What is correct in this situation?

You are at an intersection with a yellow diamond sign, which means you are on a priority road. The motorbike approaching from the right is coming from a less important road. According to German traffic rules, vehicles on the priority road have the right of way, and vehicles entering from side roads must wait.

Since you are driving on the priority road, you have the right of way over the motorbike. Therefore, the motorbike must wait, but the correct answer was that you have to allow the motorbike the right of way (option 1). This can seem confusing, but the key detail here is the road sign below the priority sign—it's a priority road with an intersection where you must consider the given road layout.

In German rules, sometimes in complex intersections, even vehicles on a priority road need to give way if directed by specific traffic signs or if other lane or crossing rules apply.

In this image, the sign with the T-intersection symbol clarifies which side has priority at the crossing. The motorbike is on the priority road going straight, while you are turning left and crossing the motorbike's path. In general, when turning left, you must allow oncoming traffic to go straight first.

So the rule is: When turning left at an intersection, you must give way to oncoming traffic, even if you are on a priority road. This is why you must allow the motorbike to go first. Your answer is correct, and the relevant rule is that left-turning vehicles must yield to oncoming traffic going straight or turning right.