Brake lights flicker while driving

Hello! Last Thursday a driver standing next to me at the traffic light pointed out that when driving the brake light flickered. I then checked this with my wife, and it was really so that when driving the two brake lights went synchronously from time to time. They then flickered short and went out again and so on. However, at no point during driving any control lights lit up. I drove to the FOH and could not find anything. I unfortunately could not check it there, because I remained in the car because I was paralysed. At home the error showed up again and moreover a brake light no longer went. Probably the error existed longer and now the constant flickering destroys the one lamp, the next one will probably soon follow. Has anyone of the revered readership already experienced similar things, or has any idea what that could be? I should bring the car into the workshop the day after tomorrow and I have the fear that one replaces half the car until one finds the mistake, the Master already knew on the phone that the brake switch was helpful.