list posts of two post types in a single template

As I already mentioned in my comments, you must use pre_get_posts to add custom post types to archive pages.

One thing you must keep in mind here though, you have two archive pages here, archive.php and archive-event.php, so is_archive() is going to return true on both, which will alter both pages. You will need to exclude archive-event.php from your function. To do this, you’ll need to make use of is_post_type_archive() to check and exclude that specific page

For all the possible parameters you can use with pre_get_posts, go have a look at WP_Query

function cpt_in_archive($query) {
  if ( !is_admin() && $query->is_main_query() && $query->is_archive() && $query->!is_post_type_archive( 'event' )) {

      $query->set( 'post_type', array( 'post', 'event' ) );
      $query->set( 'orderby', 'date' );

   }
}

add_action( 'pre_get_posts' , 'cpt_in_archive' );