ETA: I installed third part software from the beginning.

I've updated the Intel drivers:

sudo add-apt-repository ppa:ubuntu-x-swat/updates

sudo apt-get update

sudo apt-get upgrade

sudo apt install mesa-utils

After restarting the computer:

glxinfo | grep "OpenGL version" glxgears

The information shown by Terminal seems to be OK, but still the brightness control doesn't work.

Hope everyone is doing fine. I've recently upgraded my laptop, Ubuntu 14.04 LTS to Ubuntu 20.04 LTS. I've installed Unity Desktop and have realized that the brightness control (System settings - Brightness & Lock) is not working. When I try to change the brightness using the bar, nothing changes.

Does anyone know how to solve it?