Why is DbDependency not working?

Question

Yii

Good afternoon.
Need help cache is working fine.
But I can’t understand DbDependency either it works, or no,
I need the table to be updated when updated_at changes.
What's wrong, who knows?

$db = User::getDb();
        $dep = new DbDependency();
        $dep->sql = "SELECT MAX(updated_at) FROM user";
        $result = $db->cache(function ($db) {
            return User::find()->all($db);
        }, 600, $dep);