For a long time. I used a shell script to brighten and dim my laptop monitor, because the Fn+F5 and Fn+F6 combinations did not work.¹¹ From what I could tell, X11 didn’t understand keys were pressed at all. I remember fixing it, but I’m not sure what I did to fix it. While looking for stuff to include in my backups, I discovered /etc/X11/xorg.conf.d/40-video.conf which contains

Section "Device"
    Identifier  "Card0"
    Driver      "intel"
    Option      "Backlight"  "intel_backlight"
    Option      "SWcursor"
EndSection

This may or may not be part of the solution. I have also changed /etc/default/grub to include²² where my addition is the last part of the string, i.e. acpi_osi=

GRUB_CMDLINE_LINUX_DEFAULT="quiet acpi_osi="

I have some vague memory of this being relevant as well.

So there you go. May or may not work. Might not be needed at all these days! Linux evolves surprisingly quickly when you are not waiting for a particular feature.