What is the right course of action?

Your chosen actions are correct because, according to German traffic rules, when approaching an obstruction like a slow-moving vehicle on a single-lane road, you should first reduce your speed and wait patiently if overtaking is not immediately possible or safe. Slowing down helps maintain safe following distance and control, especially in poor weather conditions. Switching lanes prematurely or without clear safe opportunity is not advised, especially if the road is narrow or visibility is limited. The rule emphasizes caution, patience, and adapting speed to the situation before attempting to pass. This approach helps prevent accidents and ensures smooth traffic flow.