Hello I was wondering if anyone is having this same issue as I am, I am currently unable to change my brightness level on my laptop using the keyboard combinations to change the brightness level but I am able to do so with the slider with power manager settings (while using Gnome as DE the brightness applet won't work either).
I already change the grub kernel parameters to "quiet acpi_osi=Linux acpi_brightness=vendor splash" and all the similar combinations that people often suggest and I had no luck (actually those made it impossible to change the brightness even in the power manager settings).
Typing in a terminal...
pkexec /usr/sbin/gnome-power-backlight-helper --set-brightness 1
makes my brightness to go the lowest level and...
pkexec /usr/sbin/gnome-power-backlight-helper --set-brightness 10
the highest level.
I was wondering if anyone has had this same issue. I don't know if this helps but while using Fedora this issue does not happens, brightness keys will work perfectly fine.