Display reusable blocks in WP backend

reusable-block-admin-menu.php

/**
 * Reusable Blocks accessible in backend
 * @link https://www.billerickson.net/reusable-blocks-accessible-in-wordpress-admin-area
 *
 */
function mrco_reusable_blocks_admin_menu() {
	// Add under Appearence nav. 
    add_submenu_page( 'themes.php', 'Reusable Blocks', 'Reusable Blocks', 'edit_posts', 'edit.php?post_type=wp_block', '' );
    // Remove it if still exists at top level. 
    remove_menu_page( 'edit.php?post_type=wp_block' );
}
add_action( 'admin_menu',  'mrco_reusable_blocks_admin_menu' );