What is the right behaviour now?

At a red traffic light, you must always stop and wait until the light turns green before proceeding. This rule applies regardless of whether other vehicles nearby are moving or waiting, or whether a truck next to you drives on. You are only allowed to drive on when your own traffic light shows green. Selecting "off now" (answer 1) is correct in this situation, because as your light is red, you must remain stopped. This is a fundamental traffic rule for intersections in Germany and helps prevent collisions and confusion. Always pay attention to your own traffic signal and act accordingly.