helpers.php

<?php
/**
 * Get a reusable block by its title.
 *
 * @param string $title             The post title of the reusable block.
 * @param bool   $filter_results    Whether the results should be filtered through the_content filter.
 * @return string|null              The reusable block content if found, null otherwise.
 */
function get_reusable_block( $title, $filter_results = true ) {

	$query = new WP_Query(
		array(
			'post_type' => 'wp_block',
			'title'     => $title,
		)
	);

	if ( empty( $query->post ) ) {
		return null; // No reusable block found.
	}

	$reusable_block = $query->post;

	if ( $filter_results ) {
		return filter_reusable_block_content( $reusable_block->post_content );
	}

	return $reusable_block->post_content;
}

/**
 * Apply the_content filter to the given reusable block content.
 *
 * @param string $content    The reusable block content.
 * @return string            The filtered content.
 */
function filter_reusable_block_content( string $content ): string {
	return apply_filters( 'the_content', $content );
}