What is true about using the hard shoulder in this situation?

Answer 1 is correct. In Germany the hard shoulder is normally not a driving lane, but it can be temporarily “released” as an extra lane (Standstreifenfreigabe). When this happens, you must treat it like a normal right-hand lane: you may drive on it, you must follow the same speed limit and lane discipline, and you should expect vehicles to enter and leave it where it begins/ends.

That’s why answer 2 is wrong in this situation: it’s not restricted to breakdowns if the authorities have opened it for traffic. And answer 3 is wrong because it’s not “only for trucks” either; if it’s opened, it’s generally for all vehicles allowed on the motorway unless a specific restriction is shown.

Rule of thumb for similar questions: hard shoulder equals “emergency only” unless a sign or electronic lane control explicitly turns it into a usable lane; once opened, it behaves like the rightmost lane.