oliverdavies.uk-drupal-old/web/modules/custom/blog/opdavies_blog.install

<?php

declare(strict_types=1);

use Drupal\opdavies_blog\Repository\PostRepository;

/**
 * Mark existing blog posts as sent to social media.
 */
function opdavies_blog_update_8001(): void {
  $posts = \Drupal::service(PostRepository::class)->getAll();

  foreach ($posts as $post) {
    $post->set('field_sent_to_social_media', TRUE);
    $post->save();
  }
}