NixOS-Config/modules/system/services/pc/keyd/default.nix

{ ... }:
{
  services.keyd = {
    enable = true;
    keyboards.default = {
      ids = [ "*" ];
      settings = {
        main = {
          capslock = "overload(control,esc)";
          esc = "capslock";
          rightcontrol = "esc";
          leftcontrol = "noop";
          left = "noop";
          down = "noop";
          up = "noop";
          right = "noop";
        };
        control = {
          h = "left";
          j = "down";
          k = "up";
          l = "right";
        };
      };
    };
  };
}