How to add new rule in laravel validations in Laravel 8?

Add new rules in laravel validations in Laravel 8

//Rule

use Illuminate\Validation\Rule;   

      $validator = Validator::make($request->all(), [

            'email' => 'required|unique:users|max:255|email:rfc,dns',

'username' => [

'required','min:4',

Rule::unique('users')->where(function ($query) {

$query->where('is_verified','=', '1');

return $query;

})

],

            'displayname' => 'required',

            'password' => 'required',

        ],$messages = [], [

            'email' => 'Email',

            'username' => 'Username',

            'displayname' => 'Display Name',

            'password' => 'Password',

        ]);