It depends on the environment brightness. Hold your thumb on top of the display border, left of the ear speaker, and wait a few seconds; the screen should darken.
In my opinion, the setting is still much too bright when you are in a dark room and have a lamp on.
The behaviour of the adaptive brightness is now just different from my XA2 Plus. With the XA2 plus i can immediately see the brightness to change (lower or highter). with the c2 i cannot see any change at all. Or is it possible to change the brightness without the adaptiveness? I do not need adaptive brightness, i would like to change the brightness myself. That would be nice.
Go to Preferences - Display and tick first option off, after that you can use the dropdown-menu like nephros posted the screenshot above this post to select it
To me it seems that the HW analog amplification is set to high as light sensor goes to max (CSD reports 16383) in moderate light conditions and in really low light there is still too high value.