xbacklight: No outputs have backlight property - No /sys/class/backlight folder

Check your /sys/class/backlight folder. If you can see an intel_backlight folder there and still you are getting the above error then creating a /etc/X11/xorg.conf file with the below configuration should work for you. It worked for me.

Section "Device"
    Identifier  "Intel Graphics" 
    Driver      "intel"
    Option      "Backlight"  "intel_backlight"
EndSection

Also, remember to logout and login again for the changes to take effect.

Reference: Backlight - ArchWiki

That is completely normal. To find the directory for your backlight settings, do this:

sudo find /sys/ -type f -iname '*brightness*'

The output should give you something like this:

/sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-LVDS-1/intel_backlight/brightness

Now, all you have to do is link it to /sys/class/backlight. To do that:

sudo ln -s /sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-LVDS-1/intel_backlight  /sys/class/backlight

If you still get the error, then do this:

Create the file xorg.conf:

sudo nano /etc/X11/xorg.conf

And add these lines:

Section "Device"
Identifier  "Card0"
Driver      "intel"
Option      "Backlight"  "NAME OF THE FOLDER"
EndSection

Then, to save the file do: Ctrl + X then Y then Enter.

Also, for the Driver part check for your configuration, i.e., acpi_video0 or intel_backlight.

Every step required for xbacklight control

Follow these steps:

1. $ sudo nano /etc/default/grub and replace the corresponding line with GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_backlight=vendor"
2. $ sudo update-grub
3. No joking, make sure that the appropriate drivers are actually installed: $ sudo apt install xbacklight xorg xserver-xorg-video-intel
4. Issuing $ find /sys -type f -name brightness should yield something like /sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-eDP-1/intel_backlight/brightness
5. $ cd /sys/class This directory should contain a soft link called brightness to the brightness device discovered in the previous step. Should it be missing, create it: $ sudo ln -s /sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-eDP-1/intel_backlight/brightness /sys/class/brightness
6. $ sudo nano /etc/X11/xorg.conf should read:

Section "Device"
    Identifier      "Device0"
    Driver          "intel"
    Option          "Backlight"      "intel_backlight"
EndSection

Section "Monitor"
    Identifier      "Monitor0"
EndSection

Section "Screen"
    Identifier      "Screen0"
    Monitor         "Monitor0"
    Device          "Device0"
EndSection

7. The assignment of the physical XF86MonBrightnessDown and XF86MonBrightnessUp keys is explained here for Xubuntu LTS or XFCE users.
8. Finally, reboot for these changes to take effect.