Sometimes Google is just not enough. Especially when you’ve clicked hundreds of results, hoping you will find the right answer to your problem. My problem was the Matrox G550 video card and its missing drivers for the modern, nowadays versions of Linux. In my case, the distro is Ubuntu.
I have tried to do everything I found on Google about how to set up X in order to display on dual monitor configuration. After hours of trying almost everything, I have combined all information I found and managed to find the workaround for Matrox G550 dual monitor configuration.