preprocessors-8.x-1.0-beta8/modules/preprocessors_example/src/Plugin/preprocessors/NodeBundlePreprocessor.php

<?php

namespace Drupal\preprocessors_example\Plugin\preprocessors;

use Drupal\preprocessors\Attribute\Preprocessor;
use Drupal\preprocessors\PreprocessorPluginBase;

/**
 * Provide plugin to preprocess variables for nodes of a given bundle.
 */
#[Preprocessor(
  id: 'preprocessors_example.preprocessor.node_bundle',
  hooks: [
    "node__bundle"
  ],
  themes: "*",
  weight: 0
)]
final class NodeBundlePreprocessor extends PreprocessorPluginBase {

  /**
   * Preprocess your variables.
   *
   * This method works just like a 'hook_preprocess_HOOK()' function.
   *
   * {@inheritdoc}
   */
  public function preprocess(array &$variables, string $hook, array $info) : void {
    $variables['foo'] = "bar";
  }

}