I've tried a few different combinations as well. I've also defined several different options all at once. I've also tried: GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_osi= acpi_backlight=intel GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_osi="
I have edited the grub file as below and after updating grub I've done a reboot. Specifically, I have followed the many suggestions that were recommended from this link with no luck. Specifically the key combinations for adjusting keyboard backlight for my model FN+F3 to dim and FN+F4 to brighten. Some of the F# keys do not respond their dedicated function when holding the Fn key. I'm having quite the time getting my keyboard backlights to work on my ROG Zephyrus laptop.