Monitor brightness?

I bought a new Samsung monitor to play with the Xbox. He always turns the brightness up and down in games. So that automatically adjusts. It is very annoying to gamble. Can you issue that? I've already tried everything on the monitor via settings but there's nothing.
Use it only for Xbox one x

More accurate model

Samsung u28r554uqu

Try switching off the "video optimization" in the settings.

Maybe there's no option, got the idea of a different model type

Maybe it's Samsung Magic bright

Game mode on "always on", then this magic bright should be off.

(Is in the instruction manual)

Unfortunately does not work, have always turned on light and dark all the time. Mega annoying

Unfortunately I have no more ideas. It may also be a defect