Who has priority here?

You answered correctly. The yellow diamond sign with a black border indicates you are on the priority road. However, there is also an additional sign showing that the side street to the right has to yield. Despite being on the priority road, you must give way to vehicles approaching from the right at intersections when turning left, unless the road marking or traffic sign instruct otherwise.

In this case, the electric scooter is coming from your right, and German traffic rules state that vehicles from the right have priority at intersections unless otherwise marked. The electric scooter does not have a stop or yield sign, so it has priority. The truck needs to yield because it is coming from the left and does not have the priority in this situation.

So, only the electric scooter has priority here. Remember: In unclear situations at intersections, always check for traffic from your right and who is on the priority road, and watch for additional signs clarifying the right of way.