Detect whether a block has server-side render

In PHP, it’s certainly possible to check if a block type is dynamic or whether the block uses server-side rendering. For example for already registered block types, just get the block type object and call its is_dynamic method.

$block_registry = WP_Block_Type_Registry::get_instance();

$block_name="core/latest-posts";
$block_type_object = $block_registry->get_registered( $block_name );

if ( $block_type_object ) {
    // Note: render_callback is not included in the REST API response.
    var_dump(
        $block_name,
        $block_type_object->is_dynamic(),
        $block_type_object->render_callback
    );
}

In Gutenberg though, for now you would need to fetch the block type object/data from the Block Types API endpoints, and just check whether the block type’s is_dynamic property is true.

But you could combine PHP and JS: Add a constant/variable which stores the names of the dynamic block types, and in checkServersideRender(), just check whether settings.name is in the list.

Example using get_dynamic_block_names() and wp_add_inline_script():

• PHP:

  add_action( 'enqueue_block_editor_assets', 'my_enqueue_block_editor_assets' );
  function my_enqueue_block_editor_assets() {
      wp_add_inline_script(
          'wp-blocks',
          sprintf(
              'const DYNAMIC_BLOCKS = %s;',
              wp_json_encode( get_dynamic_block_names() )
          )
      );
  }
  

• JS:

  const checkServersideRender = ( settings ) => {
      if ( DYNAMIC_BLOCKS.indexOf( settings.name ) >= 0 ) {
          // it's a dynamic block type; add your attributes
      }
  
      return settings;
  };
  

But then, for what you’re trying to do, it’s probably better/easier to just add your custom attributes using the register_block_type_args hook. That way, you wouldn’t need to worry about breaking server-side rendered blocks, or that you would be free from the rest_invalid_param error as stated in the previous revision.

add_filter( 'register_block_type_args', 'my_register_block_type_args' );
function my_register_block_type_args( $args ) {
    $args['attributes']['your_attribute'] = array(
        'type'    => 'boolean',
        'default' => false,
    }

    return $args;
}