What is the right course of action now?

You answered correctly. On rural roads in Germany, especially when wide vehicles like trucks approach in the oncoming lane, you should drive as far to the right as safely possible to maximize the space between your vehicle and the oncoming one. This helps avoid side collisions and gives both drivers more safety margin.

Braking is also correct, as it reduces speed and gives you more time to react if something unexpected happens, such as the truck being very wide or moving close to the center line. Slowing down ensures better control and safety in situations with narrow space.

It is not correct to change direction to the left because that would bring you closer to oncoming traffic, which increases the risk of a head-on collision. Always stay to the right and reduce speed if necessary when passing large vehicles on narrow rural roads. This is a basic rule for safe driving in such situations in Germany.