Render user avatar with image style

if ($message_owner->user_picture && !$message_owner->user_picture->isEmpty()) {
 $render_array = [
   '#theme' => 'image_style',
   '#style_name' => 'privatemsg_avatar',
   '#uri' => $message_owner->user_picture->entity->getFileUri(),
   '#alt' => $message_owner->getDisplayName(),
 ];
 $rendered_image = \Drupal::service('renderer')->render($render_array);
}