Looping lists in chunks/batches, as mentioned here http://blog.ign.uy/2017/loop-list-in-batches-using-twig

array_chunk-example.php

<?php foreach (array_chunk($photoList, 2) as $photos): ?>
  <div class="grid-row">
  <?php foreach ($photos as $key => $photo): ?>
    <div class="grid-overlay__img-container">
      <div class="grid-overlay__img" data-src="<?= $photo['url_full'] ?>"></div>
    </div>
  <?php endforeach; ?>
  </div>
<?php endforeach; ?>