Screen Brightness Issues on Lenovo Legion 5 pro 2021 (ubuntu 20.04)

If your BIOS is set to dynamic / hybrid mode

Edit grub’s config:

sudo vim /etc/default/grub

Change the line:

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"

To:

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash video.use_native_backlight=1"

Then run:

sudo update-grub

And restart the laptop.
(source: VV0JC13CH)

NB if you’re experiencing screen flickering try downgrading nvidia’s driver from v495 to v470

If your BIOS is set to discrete mode (with nvidia driver)

Edit grub’s config:

sudo vim /etc/default/grub

Change the line:

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"

To:

GRUB_CMDLINE_LINUX="nvidia-drm.modeset=1 acpi_backlight=native nvidia.NVreg_RegistryDwords=EnableBrightnessControl=1"

Then run:

sudo update-grub

And restart the laptop.
(source: BertRAMAerts here)