OK I have found the error. Brightness does work but the first reading can be buggy. Put yourself in a very dark room put autobrightness to off and put the brightness level to max and put back autobrightness to on. This will never reduce the brightness. However turn a light on put the phone under it and here you can see that autobrightness is working and when you turn back off the light, the brightness level goes to the level it should have been in the first place when you turned on autobrightness.
OK I have found the error. Brightness does work but the first reading can be buggy. Put yourself in a very dark room put autobrightness to off and put the brightness level to max and put back autobrightness to on. This will never reduce the brightness. However turn a light on put the phone under it and here you can see that autobrightness is working and when you turn back off the light, the brightness level goes to the level it should have been in the first place when you turned on autobrightness.