Rest resource, GET image file in desired "Image style", by file id route parameter, and image_style_name url query parameter

ImageStyledResource.php

<?php

declare(strict_types=1);

namespace Drupal\custom_fs\Plugin\rest\resource;

use Drupal\Core\Entity\EntityTypeManagerInterface;
use Drupal\Core\StringTranslation\TranslatableMarkup;
use Drupal\rest\Attribute\RestResource;
use Drupal\rest\Plugin\ResourceBase;
use Drupal\rest\ResourceResponse;
use Psr\Log\LoggerInterface;
use Symfony\Component\DependencyInjection\ContainerInterface;
use Symfony\Component\HttpFoundation\RequestStack;

/**
 * Represents ImageStyledResource.
 */
#[RestResource(
  id: 'custom_fs_imagestyled',
  label: new TranslatableMarkup('ImageStyled'),
  uri_paths: [
    'canonical' => '/api/custom-fs-imagestyled/{id}', // ?image_style_name=thumbnail
  ],
)]
final class ImageStyledResource extends ResourceBase {

  /**
   * {@inheritdoc}
   */
  public function __construct(
    array $configuration,
    $plugin_id,
    $plugin_definition,
    array $serializer_formats,
    LoggerInterface $logger,
    private readonly EntityTypeManagerInterface $entityTypeManager,
    private readonly RequestStack $requestStack,
  ) {
    parent::__construct($configuration, $plugin_id, $plugin_definition, $serializer_formats, $logger);
  }

  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition): self {
    return new self(
      $configuration,
      $plugin_id,
      $plugin_definition,
      $container->getParameter('serializer.formats'),
      $container->get('logger.factory')->get('rest'),
      $container->get('entity_type.manager'),
      $container->get('request_stack'),
    );
  }

  /**
   * Responds to GET requests.
   */
  public function get($id): ResourceResponse {
    // Load file by id.
    $file = $this->entityTypeManager->getStorage('file')->load($id);
    // Get the original image URI.
    $original_image = $file->getFileUri();
    // Get the image style name.
    $image_style_name = $this->requestStack->getCurrentRequest()->query->get('image_style_name');
    if (!$image_style_name) {
      $image_style_name = 'thumbnail';
    }
    // Load the image style.
    $style = $this->entityTypeManager->getStorage('image_style')->load($image_style_name);

    // Get the styled image derivative.
    $destination = $style->buildUri($original_image);
    $image_styled_url = $style->buildUrl($original_image);

    // If the derivative doesn't exist yet (as the image style may have been // added post launch), create it.
    if (!file_exists($destination)) {
      $style->createDerivative($original_image, $destination);
    }

    return new ResourceResponse($image_styled_url);
  }

}