What is correct in this situation?

Your answer is fully correct. According to German traffic rules, you are allowed to drive on the advisory bike lane only if you have ruled out any risk to cyclists by carefully observing the road traffic situation. This means you must check both sides for any cyclists before using the bike lane. Additionally, you may drive on the advisory bike lane only until you have passed the truck. After that, you should return to the main lane.

These rules ensure the safety of cyclists while allowing you to safely overtake slower vehicles like trucks where the road is narrow and there is an advisory bike lane, which is not a mandatory bike lane but one that is used for easier sharing of the road. This balance between caution and flexibility is key for safely navigating such traffic situations.