Demo of Genesis Custom Blocks - A simple custom block delivered in a plugin. https://www.damiencarbery.com/2020/09/demo-of-genesis-custom-blocks/

block-accordion-block.php

<details class="genesis-custom-block <?php block_field('className'); ?>">
<summary class="item-title"><?php block_field( 'title' ); ?></summary>
<div class="item-content"><?php block_field( 'content' ); ?></div>
</details>

block-title-subtitle-block.php

<div class="genesis-custom-block <?php block_field('className'); ?>">
<h3 class="item-title"><?php block_field( 'title' ); ?></h3>
<div class="item-subtitle"><p><?php block_field( 'subtitle' ); ?></p></div>
</div>

gcb-accordion-block.php

<?php
/*
Plugin Name: Accordion block - Genesis Custom Blocks
Plugin URI: https://www.damiencarbery.com
Description: A simple accordion block created with Genesis Custom Blocks plugin.
Author: Damien Carbery
Version: 0.1
*/


add_filter( 'genesis_custom_blocks_template_path', 'dcwd_gcb_accordion_block_template_path', 10, 2 );
function dcwd_gcb_accordion_block_template_path( $path, $template_names ) {
	//error_log( 'Path: ' . var_export( $path, true ) );
	//error_log( 'Template names: ' . var_export( $template_names, true ) );
	
	foreach ( (array) $template_names as $template_name ) {
		// If the Accordion block (preview or front end), return this directory.
		if (( 'blocks/block-accordion-block.php' == $template_name ) ||
		    ( 'blocks/preview-accordion-block.php' == $template_name )) {
			return __DIR__;
		}
	}
	
	return $path;
}

gcb-title-subtitle-block.php

<?php
/*
Plugin Name: Title/Subtitle block - Genesis Custom Blocks
Plugin URI: https://www.damiencarbery.com
Description: A simple title/subtitle block created with Genesis Custom Blocks plugin.
Author: Damien Carbery
Version: 0.1
*/


add_filter( 'genesis_custom_blocks_template_path', 'dcwd_gcb_title_subtitle_block_template_path', 10, 2 );
function dcwd_gcb_title_subtitle_block_template_path( $path, $template_names ) {
	foreach ( (array) $template_names as $template_name ) {
		if ( 'blocks/block-title-subtitle-block.php' == $template_name ) {
			return __DIR__;
		}
	}
	
	return $path;
}

preview-accordion-block.php

<details open="true" class="genesis-custom-block <?php block_field('className'); ?>">
<summary class="item-title"><?php block_field( 'title' ); ?></summary>
<div class="item-content"><?php block_field( 'content' ); ?></div>
</details>