Hello. Tried every tutorial and install of nvidia graphics, putting them into config file etc with 0 results. every time i boot my nixos it hangs with underscore flashing so its a graphic card drivers issue
i have NVIDIA 4070 super
Can somene provide me with configuration.nix file that will work out from the box with this graphic card ? My Intel i5 13400f doesnt have a build in graphic.
And can you expalin how live usb have GUI and after install its not booting the same way ?
Hello 
Have you tried the RTX SUPER on NixOS stable config from the Wiki? From what I see there, you need to add a special config for the 4070 SUPER to work.
The live USB system loads graphics normally because it uses the open source nouveau drivers (which don’t need configuration) and not the proprietary Nvidia drivers.
In this regard, you could try not installing the proprietary drivers and see if your system boots normally.
Got it all working
Instructions for others that had the same issue:
when you see underscore flashing press
alt+ctrl+f2
type login you made durring instalation and password
then type
cd /nix/nixos
sudo nano configuration.nix
add command under X11windowing:
services.xserver.videoDrivers= ["nvidia"];
save the file, then type
sudo nixos-rebuild switch
and after everything install type
reboot
and it will boot into GUI