use Symfony\Component\Mailer\MailerInterface;
use Symfony\Component\Mime\Email;
use Symfony\Bridge\Twig\Mime\TemplatedEmail;

public function index(MailerInterface $mailer): Response
{
     $email = (new Email())
         ->from('from@example.com')
         ->to('to@example.com')
         ->subject('Mailer!')
         ->htmlTemplate('template.html.twig')
         ->context([
            'code' => 'foo',
            'message' => 'foo',
         ]) ;
     $mailer->send($email);
}