Public bug reported:

Backlight controls do not have any effect on a Macbook7,1 running Ubuntu 18.04.
Ubuntu is installed in Legacy BIOS mode and uses the proprietary Nvidia drivers.
The apple_backlight directory appears in /sys/class/backlight and while 
different brightness values can be set, they have no effect on the backlight's 
emitted brightness.
The backlight remains at full brightness.

I have tested the following kernel parameters but they have no effect.

acpi_backlight=vendor
video.use_bios_initial_backlight=0
acpi_osi=
video.use_native_backlight=1

** Affects: linux (Ubuntu)
     Importance: Undecided
         Status: Incomplete

** Attachment added: "acpi_backlight=vendor ls sys-class-backlight"
   
https://bugs.launchpad.net/bugs/1915082/+attachment/5461419/+files/acpi_backlight%3Dvendor%20ls%20sys-class-backlight

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https://bugs.launchpad.net/bugs/1915082

Title:
  [Macbook7,1] backlight not working

Status in linux package in Ubuntu:
  Incomplete

Bug description:
  Backlight controls do not have any effect on a Macbook7,1 running Ubuntu 
18.04.
  Ubuntu is installed in Legacy BIOS mode and uses the proprietary Nvidia 
drivers.
  The apple_backlight directory appears in /sys/class/backlight and while 
different brightness values can be set, they have no effect on the backlight's 
emitted brightness.
  The backlight remains at full brightness.

  I have tested the following kernel parameters but they have no effect.

  acpi_backlight=vendor
  video.use_bios_initial_backlight=0
  acpi_osi=
  video.use_native_backlight=1

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