Dynamically add uploaded file(s) in Symfony/Mailer

Question

I'm using the Symfony Mailer package to upload files via email. I'm using PHP 8.2 and v6.2 of symfony/mailer. My form allows users to add a maximum of 4 files for upload. The docs on file attachments show how this can be done statically but I need to add them dynamically by parsing the uploaded $_FILES array. Not surprisingly this example results in a 500 error because you can't add a loop within a method chain.

<?php

require('lib/composer/vendor/autoload.php');

use Symfony\Component\Mailer\Transport;
use Symfony\Component\Mailer\Mailer;
use Symfony\Component\Mime\Email;
use Symfony\Component\Mime\Address;

use Symfony\Component\Mime\Part\DataPart;
use Symfony\Component\Mime\Part\File;

$user = '';
$password = '';

$transport = Transport::fromDsn('smtp://' . $user . ':' . $password . '@domain.co.uk:25');
$mailer = new Mailer($transport);

$email = (new Email())
    ->from(new Address('[email protected]', 'Name'))
    ->to('[email protected]')
    ->subject('Hi this is a test using Symfony Mailer!')
    ->text('Sending emails is fun again!')
    ->addPart(new DataPart(new File('test.png'), 'Attached File'))
    ->html('<p>See Twig integration for better HTML integration!</p>');

    // Check for an uploaded file
    for($i=0; $i<=3; $i++) {

        if(!empty($_FILES['uploaded_file']['tmp_name'][$i])) {  
            $email->addPart(new DataPart(new File($_FILES['uploaded_file']['tmp_name'][$i]), $_FILES['uploaded_file']['name'][$i]));
        }           
    }

$mailer->send($email);

?>

<form method='post' enctype='multipart/form-data' action=''>
    <input class='upload_file' type='file' name='uploaded_file[]' id='upload_file1'>
    <input class='upload_file' type='file' name='uploaded_file[]' id='upload_file2'>
    <input class='upload_file' type='file' name='uploaded_file[]' id='upload_file3'>
    <input class='upload_file' type='file' name='uploaded_file[]' id='upload_file4'>
    <input type='submit'>
</form>