I have Kali Linux running on my pi-top, but I have not found a good way to adjust brightness, and when I say have not found a good way I mean "no way"
I tried xcalib and xbacklight - the sys/class/backlight folder is empty and no commands seem to change the brightness - any ideas or suggestions
when I try xbacklight - I just get "No outputs have backlight property"
Take a look here https://github.com/rricharz/pi-top-setup
I would suspect that you need to load support for the pi-top hub.