What is true in the case of this traffic sign combination?

Your answer is correct. This traffic sign combination indicates a "Yield" sign with an additional plate showing bicycle traffic coming from both directions (left and right).

According to German traffic rules, you must yield not only to motor vehicles but also to cyclists coming from either side. The presence of the bicycle symbol means you specifically need to watch out for bicycles crossing from both directions before proceeding.

Electric scooters are often treated similarly to bicycles in traffic regulations because they usually use bike lanes or paths, so you must also consider them as part of this caution.

Option 3 is incorrect because you do not only watch out for motor vehicles on the priority road but also specifically for bicycles and similar traffic. Therefore, watching out for cyclists (and electric scooters) from both directions is required here to ensure safety.