Are you allowed in this situation to use the sound signal to urge on the cyclist?

In the video you are driving along a street in a town between houses; ahead of you, in your lane, there is a cyclist, and before the junction there is sign A-7 "give way" with plate T-6c. You must not use the horn to hurry the cyclist. The answer is: no.

The Road Traffic Act allows you to use the horn only when it is necessary to warn of danger, prohibits the misuse of signals and prohibits using the horn in a built-up area, unless immediate danger requires it. A cyclist riding calmly in their lane creates no danger - it is you who must adjust your speed to them. A sudden horn behind them may frighten them: they may jerk the handlebars, swerve into the middle of the roadway or fall off, and then it is you who has caused the danger. If you want to overtake them, you do it with a gap of at least 1 m, when nothing is coming from the opposite direction, and you do not start the manoeuvre just before a junction at which you yourself must give way; if there is no room, you calmly follow them. A bicycle is a vehicle in its own right, and its rider is a road user whom the Act protects just as it protects you.

Legal basis: Art. 29 para. 1 and para. 2 point 1 and 2 and Art. 24 para. 2 of the Road Traffic Act (Prawo o ruchu drogowym)