The module create a message for all types of content

If you are using the message_example module, it is supposed to create a message for every node.

/**
 * Implements hook_node_insert().
 */
function message_example_node_insert(Node $node) {
  $message = Message::create(['template' => 'example_create_node', 'uid' => $node->get('uid')]);
  $message->set('field_node_reference', $node);
  $message->set('field_published', $node->isPublished());
  $message->save();
}