I am not 100% that it is related to the ->18.04 update, could be some other update. Nevertheless, it was a coincidence in time with the release update, so I think it might be it.
In short, this functionality: https://help.ubuntu.com/stable/ubuntu-help/display-brightness.html.en
is no longer working. I can move the slider, but brightness doesn't change. The keyboard shortcut works: it moves the slider, but the brightness doesn't change. As a temporary solution I installed and use xbacklight, but it would be nice to be able to again control brightness with dedicated hotkeys. Any advices? If nothing works, I will bind some other keys to xbacklights....
nouveau
driver (Open Source NVIDIA driver). This might be the cause. – Raffa Mar 19 '20 at 09:36sudo apt purge nvidia-*
then thissudo ubuntu-drivers autoinstall
then reboot after that. – Raffa Mar 19 '20 at 09:46