Should simpleautologout_page_attachments() logic be for logged in users only?

Thank you @noorulshameera

I am also wondering if there is any use using PrivateTempStore? From what I can see, the session time is set and then immediately called again in the next line. I have recently had a client's site go down because the tempstore was locked, causing an exception on every page.

This:

  $service = \Drupal::service('tempstore.private')->get('simpleautologout');
  $service->set('simpleautologout_session_time', time());

  $simpleautologout_session_time = $service->get('simpleautologout_session_time');

Could simply become:
$simpleautologout_session_time = time();

This would also apply to simpleautologout_user_login()

I have created a combined patch: