Zorin 17.1 on imac - missing brightness control

Hi I Installed Zorin 17.1 on 21.5" 2014 imac and there is no brightness control for the display. Night light (color temperatrure adjust) and Dark mode are different,

Prior to installing 17.1 I tested the machine on 16.3 from USB loader and the brightness control was there .
BTW it boots direct into Z17 . There is no mac OS as I formatted the internal drive hoping Zorin would install on it, no dice. I have installed on a external 1TB SSD via USB3 & it runs quite nicely. except for the brightness bug.
Its same on wayland or xorg

here is a screenshot showing missing brightness adjust slider
thanks .. Don

What GPU are you using; Nvidia?

Open Software & Updates and navigate to the Additional Drivers tab at the top:

If you have a newer driver installed like 525 and up - try a lower driver version like 470, or the Nouveau driver; had an '09 MacBook non-pro model that liked the Nouveau driver the best.

Thank you, Tried your suggestion, I was set on Nouveau , there were only 2 Nvidia drivers in my list . 390 would not load , set to 418 , still no brightness slider and now my night light is gone . Reverted to Nouveau , restart back how it was.

I wonder why my driver list isn't populated?
Also strange it worked on Z16 ?