If it wasn’t set in your initial config (fresh install), then you’d likely need to create the partition for it and enable it.
If I recall the Nixos installer (with live USB method) allows you to set that - but requires a fresh install, then just copy your config once all is set.
Have a look at nixos-hardware, there might be your device config.
Nixos ain’t much for the average Joe IMHO.
See related discussions there: NixOS is the best linux back-end ever designed. But it can't become mainstream without a front-end
Feel free to give feedback and suggest docs changes though.
Why gnome then?
gnome, kde, xfce, etc are "ready-to-go` desktop environments, so one doesn’t have to spend time setting their DE and maintaining it.
They all comes with “built-in” tools for average users (file explorer, text editor, etc).
Have you considered smth like hyprland or sway?
You would start from a minimal config then add whatever you want, instead of starting with a “bloated” config and de-bloating it.
As mention by @rhendric , avoid editing hardware-configuration.nix.