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

Your answer is correct: the hard shoulder may only be used in case of a breakdown.

In German traffic rules, the hard shoulder is primarily reserved as a safety area for emergency stops, such as vehicle breakdowns or accidents. It is not allowed to use the hard shoulder as an additional driving lane or for overtaking, even for trucks, unless explicitly allowed by traffic signs or in emergency situations.

The signs above the lanes show that the right lane (the one with a red "X") is closed, so you must move into the left or the middle lane. The hard shoulder is not to be used to bypass traffic. Using the hard shoulder as a driving lane is prohibited and can be dangerous, as it is reserved for emergencies.

Remember this rule to avoid endangering yourself and others on the road.