Return a Symfony Response Object in Drupal 9 and Drupal 8

DefaultController.php

<?php

namespace Drupal\response\Controller;

use Drupal\Core\Controller\ControllerBase;
use Symfony\Component\HttpFoundation\Response;

class DefaultController extends ControllerBase 
{
  /**
   * hello
   * @param  string $name
   * @return string
   */
  public function hello($name) {
    $response = new Response();
    $response->setContent('Hello ' . $name);
    $response->setMaxAge(10);
    return $response;
  }
}

response.info.yml

name: Response example
type: module
description: 'Return a Response Object in Drupal 8'
core: 8.x
package: Other

response.routing.yml

response.hello:
  path: '/response/hello/{name}'
  defaults:
    _content: '\Drupal\response\Controller\DefaultController::hello'
    _title: 'response Title'
  requirements:
    _permission: 'access content'

Don't forget use Symfony\Component\HttpFoundation\Response; in the controller file :)

Or use \Drupal\Core\Cache\CacheableResponse, which extends \Symfony\Component\HttpFoundation\Response adding support for cacheability meta data.