How to generate absolute URL for breadcrumbs?
You can alter the breadcrumbs of other bread crumb builders (core or contrib) in a hook_system_breadcrumb_alter():

/**
 * Implements hook_system_breadcrumb_alter().
 */
function mymodule_system_breadcrumb_alter(\Drupal\Core\Breadcrumb\Breadcrumb &amp;$breadcrumb, \Drupal\Core\Routing\RouteMatchInterface $route_match, array $context) {
  $links = $breadcrumb-&gt;getLinks();
  foreach ($links as $link) {
    $url = $link-&gt;getUrl();
    $url-&gt;setAbsolute();
  }
}