What applies here?

Your answer is correct because the police officer is giving a signal that allows you to cross the crossroads. In German traffic rules, a police officer's hand signals take precedence over traffic lights and signs. When the officer's arms are positioned as in the image (standing sideways to you with one arm extended), it means you may proceed across the junction.

You do not have to wait for any further signals, nor is turning off prohibited just based on this situation. The main point is to follow the officer's instructions, which here clearly permit crossing safely. This rule helps manage traffic flow efficiently and ensures safety at intersections where police officers are directing traffic.