@omz, I am not sure if this points to an issue or not. But I use your Sample code in my startup script to change the brightness of the screen. It had been working perfectly.

from objc_util import *
UIScreen = ObjCClass('UIScreen')

screen = UIScreen.mainScreen()
screen.setBrightness_(0.2)

Now when my ipad goes to sleep and then I wake it, it's not retaining the brightness setting. Again, I am not sure just my ipad pro or something you need to check or maybe the sample code is out of date. I copied it sometime ago.