functions.php

<?php

/**
 * Get service sections
 * @see https://www.billerickson.net/access-gutenberg-block-data/
 */
function ea_get_service_sections() {

	$sections = array();

	global $post;
	$blocks = parse_blocks( $post->post_content );
	foreach( $blocks as $block ) {
		if( 'acf/service' !== $block['blockName'] )
			continue;

		$title = $anchor = '';
		if( !empty( $block['attrs']['data']['title'] ) )
			$title = $block['attrs']['data']['title'];

		if( !empty( $block['attrs']['data']['anchor'] ) )
			$anchor = $block['attrs']['data']['anchor'];

		if( empty( $anchor ) )
			$anchor = $title;

		$sections[] = '<a href="' . get_permalink() . '#' . sanitize_title_with_dashes( $anchor ) . '">' . esc_html( $title ) . '</a>';
	}

	if( empty( $sections ) )
		return;

	echo '<ul class="service-sections">';
	foreach( $sections as $section )
		echo '<li>' . $section . '</li>';
	echo '</ul>';
}