Google indexes the page using the domain alias
It really depends on what page Google finds first, I guess. So, I do now know. 


  Why is the alias shown in Google search results, and not the root domain?


However in order to overcome this, you would have used the global redirect in Drupal 7, which has been merged with Redirect. I have not tried it, but if it an exact port it should still be able to. 


  Checks if the current URL is the same as the site_frontpage and
  redirects to the frontpage if there is a match.