Screen Brightness Changes Depending on Screen Contents - how do i turn it off?
Solution 1:
One of the similar questions actually solved my problem: It is a feature of the intel graphics driver and it's well hidden.
It has been solved by this answer by @zeel but i'm adding it here in case anyone comes our way from a search engine.
Intel:
Intel system tray icon > Graphics Properties > Power > On Battery > Display Power Saving Technology -> turn it off.