Keyboard Customization in NixOS

in configuration.nix:

  services.xserver = {
    # https://nixos.org/manual/nixos/stable/options#opt-services.xserver.enable
    enable = true;
    desktopManager.gnome.enable = true;
    displayManager.gdm.enable = true;
  };

  # Configure keymap in X11
  services.xserver.xkb = {
    layout = "us";
    variant = "";
    options = "ctrl:swapcaps";
  };

Build it normally with sudo nixos-rebuild switch.

sudo nixos-rebuild boot
sudo reboot

Then run these:

gsettings reset org.gnome.desktop.input-sources xkb-options
gsettings reset org.gnome.desktop.input-sources sources

Then reboot.