index-main/site/snippets/blocks/gallery.php

<?php
/** @var \Kirby\Cms\Block $block */
$images      = $block->images()->toFiles();
$imgSizes    = $imgSizes    ?? '(min-width: 768px) 50vw, 90vw';
$imgSrcset   = $imgSrcset   ?? 'body-half';
?>

<div class="swiper">
    <div class="swiper-wrapper">
        <?php foreach ($images as $image): ?>
        <div class="swiper-slide">
            <figure>
                <?php snippet('picture', [
                    'file'       => $image,
                    'alt'        => $image->alt()->value(),
                    'sizes'      => $imgSizes,
                    'srcsetName' => $imgSrcset,
                    'lazy'       => true,
                ]) ?>
                <?php if ($image->caption()->isNotEmpty()): ?>
                <figcaption><?= $image->caption()->html() ?></figcaption>
                <?php endif ?>
            </figure>
        </div>
        <?php endforeach ?>
    </div>
    <div class="swiper-button-prev"></div>
    <div class="swiper-button-next"></div>
    <div class="swiper-pagination"></div>
</div>