Can't change screen brightness on ubuntu 20.04 (Always display maximum brightness)

Question

I'm new to linux and this is my first installation of ubuntu 20.04 on ASUS ROG ZEPHYRUS G14 laptop. After installation, I can't change the screen brightness and my screen always show the highest screen brightness. After some time of changing grub in ubuntu forum, this is my attempts

Add acpi_brightness=vendor or acpi_backlight=native or acpi_backlight=native or acpi_backlight=none to grub etc/default/grub still not working
After that I installed brightness-controller-simple and brightness-controller and slide the brightness control to minimum and my screen brightness stays the same
I installed xbacklight and run this command xbacklight -set 50 still didn't work

Note : I manged to install nvidia drivers on my laptop after using nouveau for 2 days
and this is my result after run this command ls /sys/class/backlight/acpi_video0 >>> actual_brightness  brightness  max_brightness  scale      type bl_power           device      power           subsystem  uevent
My laptop specs : CPU : AMD Ryzen 7 4800HS
GPU : NVIDIA GeForce GTX 1650 Ti 4GB GDDR6
RAM : 16 GB
Kernel : Linux 5.4.0-42-generic #46-Ubuntu SMP Fri Jul 10 00:24:02 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux

Dipanshu · Answer

I have the same laptop, same situation. Finally found the solution to be an upgrade to a new linux kernel.
Ubuntu 20.04 came with 5.4.x, Installing 5.7.15 fixed it for me. The hotkeys for brightness control still didn't work with fn but I mapped the  f7 and f8 to that as I don't use them often.
Don't try to compile linux kernels yourself if you're not sure how that works, just use mainline. You might have to disable secureboot from the bios for some of the kernel versions. I had to disable it for 5.7.15
A comprehensive discussion for some other problems with this setup can be found at this reddit post

Can't change screen brightness on ubuntu 20.04 (Always display maximum brightness)

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