Should you use the horn in the presented situation, in order to warn the cyclist of your intention to overtake?

Buildings and pavements are visible in the recording, which indicates that you are moving in a built-up area. According to Art. 29 para. 2 of the Road Traffic Act, using a sound signal in a built-up area is prohibited unless it is necessary in connection with an immediate danger. Since the cyclist is riding correctly and does not pose a threat, you do not have the right to use the horn solely to warn them of overtaking.