In the presented situation, is it mandatory to stop before entering this intersection?

Why?

The A-7 “Give way” sign before the roundabout does not require you to stop every time. You must take particular care and give way to vehicles already on the roundabout. If you can enter safely without obstructing traffic that has priority, you do not have to stop.

§ 5 ust. 5 oraz § 36 ust. 2 rozporządzenia w sprawie znaków i sygnałów drogowych