Xbacklight not working after setting up proprietary Nvidia drivers

Hi,
Xbacklight was working fine untill I changed from bumblebee to PRIME with NVIDIA proprietary drivers using this guide

here is the output of

/proc/cmdline

BOOT_IMAGE=/boot/vmlinuz-4.20-x86_64 root=UUID=a747ca4d-5e5b-474c-a8a5-2fde38ab19a3 rw acpi_osi=! acpi_osi=“Windows 2009” acpi_backlight=vendor resume=UUID=6b4e4449-c0a6-44d0-8188-f5df22ea6c83

Please let me know if you need any other outputs.
Thank you

Change the Kernel, Kernel 4.20 is EOL.

Is your system up to date?

sudo pacman-mirrors -f5 && sudo pacman -Syyuu