I have Lenovo Legion 5 15ARH05 with Ryzen 5 4600H. I've checked that the issue 
is present in Ubuntu 20.10 beta, Fedora 32 with Kernel 5.8, Fedora 33, Manjaro 
with latest 5.8 kernel, opensuse tumbleweed.
On manjaro and fedora 32 with any kernel 5.6, and MX Linux backlight can be 
changed at first. But it seems force shutting down the laptop (hold power 
button) immediately breaks it and upon the next boot brightness cannot be 
changed. I've reproduced this behavior in manjaro, fedora 32, and MX Linux all 
with kernel 5.6.*.

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https://bugs.launchpad.net/bugs/1861925

Title:
  BrightnessOutofRange: Actual brightness for amdgpu_bl0 not in range
  0..255

Status in Pop!_OS:
  New
Status in linux package in Ubuntu:
  Incomplete

Bug description:
  Hi,

  I have a acer aspire a315-41 laptop, it has BIOS 1.15, Ubuntu 19.10,
  Kernel stock 5.3, and 5.5.0. I have a problem with the Backlight. I
  can not control.

  According to: https://wiki.ubuntu.com/Kernel/Debugging/Backlight

  It is : Backlight control does not work, but there are entries in
  /sys/class/backlight.

  The problem is as far I could find:

  sanya@Aspire-A315-41:/sys/class/backlight/amdgpu_bl0$ cat brightness
  135
  sanya@Aspire-A315-41:/sys/class/backlight/amdgpu_bl0$ cat actual_brightness
  43500
  sanya@Aspire-A315-41:/sys/class/backlight/amdgpu_bl0$ cat max_brightness
  255

  The brightness read from the HW is not in the range, and when I change
  the brightness by the keys the value in the brightness file changes
  too, but the actual_brightness is stuck at the value 43500...

  I have tried all the steps mentioned in
  https://wiki.ubuntu.com/Kernel/Debugging/Backlight

  Actually I have tried all these kernel startup parameter variants
  without luck:

  GRUB_CMDLINE_LINUX_DEFAULT=""
  #GRUB_CMDLINE_LINUX_DEFAULT="video.use_native_backlight=1"
  #GRUB_CMDLINE_LINUX_DEFAULT="acpi_osi="
  #GRUB_CMDLINE_LINUX_DEFAULT="video.use_bios_initial_backlight=0"
  #GRUB_CMDLINE_LINUX_DEFAULT="amdgpu.dcfeaturemask=0x4 amdgpu.abmlevel=2"
  #GRUB_CMDLINE_LINUX_DEFAULT="acpi_backlight=video amdgpu.abmlevel=1"
  #GRUB_CMDLINE_LINUX_DEFAULT="i8042.nopnp acpi_osi=Linux acpi_backlight=vendor"
  #GRUB_CMDLINE_LINUX_DEFAULT="i8042.nopnp acpi_osi=! acpi_osi=\"Windows 2009\" 
acpi_backlight=vendor"
  #GRUB_CMDLINE_LINUX_DEFAULT="i8042.nopnp acpi_osi=! acpi_osi=\"Windows 2009\" 
acpi_backlight=video"
  #GRUB_CMDLINE_LINUX_DEFAULT="acpi_osi=! acpi_osi=\"Windows 2009\" 
acpi_backlight=vendor"
  #GRUB_CMDLINE_LINUX_DEFAULT="i8042.nopnp acpi_osi=! acpi_osi=\"Windows 2009\" 
acpi_backlight=vendor"
  #GRUB_CMDLINE_LINUX_DEFAULT="i8042.nopnp acpi_osi=! acpi_osi=\"Windows 2009\" 
acpi_backlight=vendor"

  I guess the fwts has found also this as an error:

  autobrightness: Automated LCD brightness test.
  
--------------------------------------------------------------------------------
  Test 1 of 2: Test for maximum and actual brightness.
  PASSED: Test 1, Maximum brightness for amdgpu_bl0 is 255 which is sane.
  FAILED [HIGH] BrightnessOutofRange: Test 1, Actual brightness for amdgpu_bl0 
not
  in range 0..255.

  Test 2 of 2: Change actual brightness.
  FAILED [MEDIUM] BrightnessMismatch: Test 2, 256 brightness levels did not 
match
  the brightnesss level just set for backlight amdgpu_bl0.
  The failed brightness levels were: 0-255.

  It would be great if someone could help set the HW brightness back to
  the normal range.

  If you need any more debug files please let me know!

  Thanks,
  Regards,
  Sandor

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