What is correct in this situation?

You were right with answer 1: you must give the motorbike the right of way.

The key rule here is “right of way on the priority road.” The yellow diamond sign means you are on a priority road. The additional sign underneath shows that the priority road bends to the right at the intersection. That means the motorbike coming from the right is also on the same priority road, while the road straight ahead (the one you would take if you continue forward) is the minor road.

So if you want to continue straight, you would be leaving the priority road. Vehicles that stay on the priority road (here: the motorbike following the bend) have priority over you, so you must wait.

Also important for similar situations: even though the road “feels straight,” you must follow the course of the priority road shown on the extra sign when deciding who has priority.