What does this traffic sign indicate?

Your choice, answer 1, is correct. This orange arrow on a rectangular sign is used on autobahns to mark a “relief route” (Entlastungsstrecke): an alternative autobahn section that is normally less busy and can be used to bypass congestion.

Rule of thumb: Orange guidance signs on the autobahn usually relate to traffic management (diversions, relief routes, congestion routing). This specific sign is not telling you to exit immediately and it is not specifically for dangerous goods vehicles. It simply indicates a recommended, typically less-used autobahn section to reduce traffic load.