I went to Nvidia website to update the driver for Nvidia 1050 Ti. I can use the function keys to change the volume but I cannot use those F5 and F6 keys to change the brightness. Could you please let me know how to fix it?
As I was in the same situation, I found compromise solution that I want to describe.
First, in order to install Ubuntu 18.01, it was first necessary to change in the BIOS the video setting from "Hybrid graphics" to "Discrete graphics" (which bricked the machine because of a bug in the BIOS, but the machine got replaced after a month, but this is another story).
Finally, with Discrete mode On, I could install Ubuntu 18.01. But then this brightness stuff didn't work. When going back into BIOS and switching to Hybrid mode, then the graphics wouldn't work.
So, I installed the proprietary (non opensource) Nvidia drivers through the "Software & Updates" Program. Rebooted, still no possibility to adjust brightness.
But now, with the proprietary Nvidia driver I can switch the BIOS setting to Hybrid mode again, and then the brightness controls work!