Are you allowed in this situation to drive into the intersection without stopping the vehicle before the presented solid line?

Why?

You must not enter without stopping because the visible B-20 STOP sign requires a complete stop. The solid transverse line P-12 marks the point before which you must stop. Simply slowing down and checking that the road is clear is not enough.

§ 21 ust. 1 i 2 oraz § 89 ust. 1 rozporządzenia w sprawie znaków i sygnałów drogowych