safekat/ci4/app/Models/UserModel.php

<?php

declare(strict_types=1);

namespace App\Models;

use CodeIgniter\Shield\Models\UserModel as ShieldUserModel;

class UserModel extends ShieldUserModel
{
    protected function initialize(): void
    {
        parent::initialize();

        $this->allowedFields = [
            ...$this->allowedFields,
            'first_name',   // Añadido
            'last_name',   // Añadido
        ];
    }

    protected $validationRules = [
        "username" => [
            "label" => "correo duplicado",
            "rules" => "is_unique[users.username]",
        ]

    ];
}