What is the right course of action?

You answered correctly that you have to wait.

The key rule here is that the motorbike is at a "No entry" sign (red circle with white horizontal bar), which means the motorbike cannot enter this street. Therefore, the motorbike must wait or turn, but since it cannot move forward, you, driving straight ahead or turning left, have the right of way.

In German traffic rules, vehicles coming from a street marked with "No entry" must not proceed, so any other vehicle already on the main road or with the proper right of way does not need to yield.

Understanding this helps you recognize situations where signs restrict entry and thus determine who must yield based on those signs, not just traffic flow or vehicle positioning.