What is the right course of action here?

You answered correctly: you must allow both the yellow car and the blue truck to go first before you proceed.

This situation is a classic example of right-before-left (“Rechts vor Links”) at an uncontrolled intersection. Vehicles coming from your right, in this case the yellow car, always have priority. Because you are turning left, you also need to wait for oncoming traffic—in this situation, the blue truck—before you can turn. Only after both vehicles have passed is it your turn to drive.

Whenever you come to an intersection without specific signs or signals, remember: yield to traffic from the right and wait for vehicles coming straight when you want to turn left. This helps avoid collisions and keeps the traffic flow safe and predictable.