No,
as far as I can see, there is nothing running in the background which is trying to get focus. Nevertheless I stopped every process which is not necessary. Nothing changed.
Btw, because of corsair iCUE is running in the background, I can see, that windows does not focus on something else. If it would, iCUE would change my keyboard color settings immediately to my default desktop theme. And I have this problem with DCS only. No other game/program is blinking away on mouse clicks.