Note: This is not a duplicate of Ubuntu 20.04 brightness adjust not working, Cannot change brightness (Ubuntu 16.04 LTS and onward) or Unable to change brightness in settings because the answers do not fix the problem.
On Dell Inspiron 11, Ubuntu 20.10, I enabled the brightness laptop keys and Settings Power panel brightness slider by adding
acpi_backlight=vendor acpi_osi=linux to
/etc/default/grub based on this post.
Following this post, I installed
$ find /sys -type f -name brightness returned:
But I was unable to add a softlink:
$ sudo ln -s /sys/devices/platform/dell-laptop/backlight/dell_backlight/brightness /sys/class/brightness ln: failed to create symbolic link '/sys/class/brightness': Operation not permitted
/etc/X11/xorg.conf with these contents:
Section "Device" Identifier "Device0" Driver "intel" Option "Backlight" "dell_backlight" EndSection
And rebooted, but the brightness does not change when I adjust the slider or use the brightness keys.
What else can I try here?