NodeBlockHooks.php

<?php

declare (strict_types=1);
namespace Drupal\node\Hook;

use Drupal\Core\Hook\Attribute\Hook;

/**
 * Block hook implementations for node.
 */
class NodeBlockHooks {
  
  /**
   * Implements hook_block_alter().
   */
  public function blockAlter(&$definitions) : void {
    // Hide the deprecated Syndicate block from the UI.
    $definitions['node_syndicate_block']['_block_ui_hidden'] = TRUE;
  }

}