No brightness control Led Cinema Display 24" El Capitan

Hi everyone,

I bought an Apple Led Cinema Display 24", used but in very good condition. If I connect the monitor to the Mac mini (late 2012) or to the MB Pro 13" (mid 2009) through mini Display Port (thunderbolt) the brightness, when turned on the mac, go to the maximum and I can't adjust it neither from the keyboard (F1 - F2) nor from system preferences.

The monitor works well but is recognized as iMac 24", not as a Led Cinema Display, even the sound is Apple USB device.

Adjustment of brightness is not activated in the preferences.

I use El Capitan version 10.11.6 (15G22010).

I had to download an app (QuickShade) that is activated at login but when I turn on and off the mac the brightness always returns to maximum.

Are there any apple updates (firmware or other) to download to make the monitor fully recognized by the operating system?

Tips?

Many thanks