What is the right course of action here?

In this scenario, the correct action is to wait until the cyclist has completed their turn. German traffic rules emphasize the importance of yielding to cyclists, especially when they are already in the process of making a maneuver. This is to ensure the safety of all road users.

By choosing to wait, you are adhering to the principle of caution and prioritizing the safety of vulnerable road users, which includes cyclists. Taking priority over the cyclist or sounding the horn could create a dangerous situation, potentially leading to an accident. Always be mindful of the traffic environment and give way appropriately when necessary.