brightness slider brightness not increasing or decreasing
Can you share a screenshot with us, is there anything else different/broken?
Did you check that "automatic brightness" is off?
i upload a video on utube u can check what do i mean ..
From what I searched (and from what's recommended in this video https://www.youtube.com/watch?v=LhvGNV8a6lQ), a third party brightness app might do the trick.