How do I add text or message above the featured image area in gutenberg for a CPT

Try this:

function wrapPostFeaturedImage( OriginalComponent ) {
    const currentPostType = wp.data.select( 'core/editor' ).getCurrentPostType();

    // Do nothing, if the post type is not rt_brands.
    if ( 'rt_brands' !== currentPostType ) {
        return OriginalComponent;
    }

    return function( props ) {
        // Your code here.
    };
}

You can also:

• Conditionally add your filter:

  // Check if the current admin page is post-new.php or post.php, and that the
  // post type of the post being added/edited is rt_brands.
  if ( 'rt_brands' === window.typenow && 'post-php' === window.adminpage ) {
      // Add your filter, i.e. call wp.hooks.addFilter().
  }
  

• Conditionally enqueue your script:

  function rt_featured_img_enqueue_script() {
      $screen = get_current_screen();
      if ( 'rt_brands' === $screen->post_type && 'post' === $screen->base ) {
          // Enqueue your featured_img.js script, i.e. call wp_enqueue_script().
      }
  }