Whole screen brightness fluctuation on both laptop/external monitor

When anything on the screen slightly moves, the brightness dips a little, and when things come back to rest, the brightness goes up again. It’s not something that shows up on the brightness control, but it’s perceivable.
It’s very annoying watching any sort of video etc, because movement will cause this whole brightness flicker thing. It’s almost like it can’t hold the brightness when something is dynamic, and then re-ups when stuff comes to rest. I’m not able to clearly put it into words, but I hope that someone could please help me with it, as it’s very annoying