Hereby, I report the Legion 5P (15ARH05H) is no longer having backlight control problems with hybrid graphics. This seem to be fixed since mid 2022 with nvidia drivers newer than version 510. In my case, I stayed with version 495.46 for a while, and did the jump to 520.56 back in October.

This change also required an update in the parameters passed to the kernel as follows,

For the nvidia drivers 495.46, I was passing:

amdgpu.backlight=0

Now, for the nvidia drivers version 520.56, I am passing:

acpi_backlight=video

This driver is working correctly with kernel versions 5.15-lts and 6.0.

Also, this laptop seems to be unaffected by the changes reported by Hans de Goede for 6.1 and 6.2.