Changes the output markup of the product blocks.

change-wc-product-block-markup.php

<?php
if (!function_exists('woo_custom_product_block_markup')) {
	function woo_custom_product_block_markup($data) {
		$product_markup = new DOMDocument();
		$product_markup->loadHTML($data);
		$product_anchor = $product_markup->getElementsByTagName('a');
		$product_id = '';

		foreach ($product_anchor as $anchor) {
			if ($anchor !== '') {
				$product_id = $anchor->getAttribute('data-product_id');
			}
		}

		$product = wc_get_product($product_id);
		// more product data...

		return '
			<li class="' . implode(' ', wc_get_product_class('', $product)) . '">
				<h3 class="title">' . get_the_title($product_id) . '</h3>
				<!-- more html -->
			</li>
		';
	}
}
add_filter('woocommerce_blocks_product_grid_item_html', 'woo_custom_product_block_markup');

More on why this is somewhat relevant here: Blocks use custom markup instead of WooCommerce templates / lack of filters