functions.php

<?php

/**
 * Block template for posts
 * @see https://www.billerickson.net/gutenberg-block-templates/
 *
*/
function be_post_block_template() {

  $post_type_object = get_post_type_object( 'post' );
  $post_type_object->template = array(
    array( 'core/paragraph' ),
    array( 'acf/ad' ),
    array( 'core/paragraph' ),
    array( 'acf/ad' ),
    array( 'core/paragraph' ),
  );
}
add_action( 'init', 'be_post_block_template' );