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

You answered correctly. This combination of traffic signs means you must yield and especially watch out for cyclists and electric scooter traffic coming from both the left and the right. The additional sign shows that bicycles (and by current rules, also electric scooters) are crossing in both directions, so special attention is needed. It does not mean that you only have to watch for motor vehicles. This is important for safely navigating intersections with special crossing rights for bikes and scooter users. Remember to always look carefully for these road users in both directions when you see this sign combination.