Comment 2 for bug 1637863

Just run the 3 lines above and here the result :
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alex@RSt:/home/alex$ sudo apt update
[sudo] password for alex:
Hit:1 http://fr.archive.ubuntu.com/ubuntu yakkety InRelease
Hit:2 http://fr.archive.ubuntu.com/ubuntu yakkety-updates InRelease
Get:3 http://security.ubuntu.com/ubuntu yakkety-security InRelease [93,3 kB]
Hit:4 http://ppa.launchpad.net/apandada1/brightness-controller/ubuntu yakkety InRelease
Fetched 93,3 kB in 0s (292 kB/s)
Reading package lists... Done
Building dependency tree
Reading state information... Done
All packages are up-to-date.
alex@RSt:/home/alex$ sudo apt install ubuntu-desktop
Reading package lists... Done
Building dependency tree
Reading state information... Done
ubuntu-desktop is already the newest version (1.373).
0 to upgrade, 0 to newly install, 0 to remove and 0 not to upgrade.
alex@RSt:/home/alex$ sudo apt full-upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
0 to upgrade, 0 to newly install, 0 to remove and 0 not to upgrade.
alex@RSt:/home/alex$
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And I rebooted.

As you can see in the lines above, in the mean time I installed 'brightness-controller' which is working fine. And even after the reboot still nothing changed (Setting and keys).

Also I attached a screenshot of the Brightness Setting.

Thanks for your help