After installing nvidia drivers using the recommended method, i rebooted my computer to see that while i am getting an output on my second monitor, my laptop display is completely dead, with a white cursor on it, which isn’t even blinking.
Thankfully with nixos you can easily reboot into the prior working configuration. 
I think most desktop environments default to mirroring two displays; this may be problematic if the displays do not support the same resolution. You have to configure the environment manually to use them in some other way.
Are you seeing this in the Linux Console, X-windows or Wayland? What Desktop Environment is installed? What output do you see on the second screen?
If you are in a Desktop Environment, find its Display configuration tool to reconfigure the displays.
If using an X-based environment, you can explore the output of xrandr to learn what display resources X finds. Possibly that also works with Wayland.