How to install pacakges from nixpkgs in config?

Help
1

I included neovim amongst the packages I install in my NixOS config:


  { config, pkgs, ... }:

  {
    nixpkgs.config.allowUnfree = true;
    system.autoUpgrade.channel = https://nixos.org/channels/nixpkgs-unstable;

    environment.systemPackages = with pkgs; [
    neovim
    firefox
    anki
    
    ulauncher

    tdesktop
    discord

    git
    python
    ruby

    neofetch
    starship
    terminus-nerdfont
    xclip
  ];
  
  environment.variables.EDITOR = "nvim"; 
  }

This stalls the nixos.neovim version of the package, which has version 4.4. I need version 5.1, which can be found in nixpkgs.neovim. I can install it with:
nix-env -iA nixpkgs.neovim

Is there a way to install it from my config?

2

I would remove the different channels that you follow, if you want the unstable package you can change the channel for your user and root

3

I follow the unstable channel. But in this channel there are two neovim packages. nixpkgs.neovim and nixos.neovim. If I specify nvim in my packages in config, I get the nixos version, but I want the other, which is more up to date.