My screen brightness doesn't work as many others have reported. So I dug around...
https://wiki.archlinux.org/title/backlight
The following ls /sys/class/backlight
generates two entries:
acpi_video0 radeon_bl0
This does nothing:
echo 20 > /sys/class/backlight/acpi_video0/brightness
This however does:
echo 20 > /sys/class/backlight/radeon_bl0/brightness
It makes me think the brightness control is targeting the wrong one. How can I fix this?