I think I know the cause, but not how to fix it: from inspecting Backlight.zig, it seems to be expecting to find the brightness properties directly under backlight, but my /sys/class/backlight contains only two symlinks: acpi_video0 and intel_backlight. intel_backlight has the correct values, but in acpi_video0 both properties are always set to 19. I confirmed that Backlight.zig is reading both properties as 19.
My computer is a System76 Galago Pro 5, running Alpine Linux edge.
Could you paste the output of the following command?
udevadm info -a /sys/class/backlight/intel_backlight | grep intel_backlight -A 12
Here it is:
looking at device '/devices/pci0000:00/0000:00:02.0/drm/card1/card1-eDP-1/intel_backlight': KERNEL=="intel_backlight" SUBSYSTEM=="backlight" DRIVER=="" ATTR{actual_brightness}=="48000" ATTR{bl_power}=="0" ATTR{brightness}=="48000" ATTR{type}=="raw" ATTR{scale}=="unknown" ATTR{max_brightness}=="48000" looking at parent device '/devices/pci0000:00/0000:00:02.0/drm/card1/card1-eDP-1': KERNELS=="card1-eDP-1" SUBSYSTEMS=="drm"