add_action( 'admin_menu', function() {
add_submenu_page(
'themes.php',
'Reusable blocks',
'Reusable blocks',
'manage_options',
'edit.php?post_type=wp_block'
);
} );
Blocks may be imported into the Code Editor view of the WordPress Block Editor (three dots in the upper-right, select code editor). This is best used as a Reusable Block, which you can dynamically add into any page or post. In order to import as a Reusable Block navigate to your site with the following URI: /wp-admin/edit.php?post_type=wp_block or see my code snippet Add reusable blocks link to the Appearance menu.
