Have a look at this old thread:
https://daemonforums.org/showthread.php?t=10177
I've had to deal with a few old, cheap and nasty Acer and Asus craptops where the backlight resisted all attempts to control it under either FreeBSD or OpenBSD. I eventually got working backlight control on one of them with Linux.
wsconsctl(8) display.brightness won't affect the backlight at all.
Most likely the backlight controls were designed around some crapware utility ms windows power management software/drivers.
I would spare yourself all the grief (not to mention your eyes) and see if a Linux distro provides working backlight controls.