Just installed Nvidia drivers on my KDE Neon (Ubuntu) and now only one monitor work on my dual monitor setup.

What do?

A simple search on your favorite search engine can sometimes save you hours ^^

At first, look into nvidia-settings.
If not working I would backup the xorg config, delete it, restart x and if it's still not working, try nvidia-xconfig. Maybe you must configure xorg by yourself, but it's easy because the internet is full of guides.

Install Windows

@RememberMe at least it has Minecraft preinstalled

@stanathen and candy crush

@git-fuckyou bloat for the win

Do go to stack overflow

Doesn't KDE have settings software for setting the number, position, and resolution of displays?