Gutenberg Reusable Block Editor Interface

wp-gutenberg-reusable-block-interface.php

function custom_add_interface_to_wp_block( $args, $post_type ) {
	global $pagenow;

	if ( 'wp_block' !== $name ) {
		return $args;
	}

	$changed_args = array(
		'show_ui'             => true,
		'show_in_menu'        => true,
		'menu_position'       => 9,
		'menu_icon'           => 'dashicons-controls-repeat',
		'show_in_admin_bar'   => false,
		'show_in_nav_menus'   => false,
		'has_archive'         => false,
		'supports'            => array( 'title', 'editor' ),
		'exclude_from_search' => true,
	);

	$args = array_merge( $args, $changed_args );

	$allowed_pages = [ 'post-new.php', 'post.php' ];
	if ( in_array( $pagenow, $allowed_pages, true ) ) {
		$args['rest_controller_class'] = 'WP_REST_Posts_Controller';
	}

	return $args;
}

add_filter( 'register_post_type_args', 'custom_add_interface_to_wp_block', 10, 2 );

I arrived here from WordPress/gutenberg#13291

I use this code to show the interface for wp_block in the menu.

The $name variable on line 4 should be changed to $post_type. And like you mentioned in the gutenberg issue: I needed to set _builtin to false.