"Handle display brightness keys" option disabled
Attempting to be able to control screen brightness, but the "Handle display brightness keys" has no toggle or radiobutton or pulldown menu.
Have not found any documentation to set this in a configuration file via the terminal. xcfe4-settings-editor has no obvious option for "Handle display brightness keys".
Same behaviour with or without acpi_backlight=video
$ cat /proc/cmdline
BOOT_IMAGE=/boot/vmlinuz-5.9.0-0.bpo.5-amd64 root=UUID=078b2cc0-b8ce-42b6-a844-796905df82b7 ro quiet acpi_backlight=video
but there still seems to be no backlight driver:
$ for interface in /sys/class/backlight/*; do echo -e "\n $interface"; cat $interface/{brightness,max_brightness,actual_brightness}; done
/sys/class/backlight/* cat: '/sys/class/backlight/*/brightness': No such file or directory cat: '/sys/class/backlight/*/max_brightness': No such file or directory cat: '/sys/class/backlight/*/actual_brightness': No such file or directory