Is is_front variable available in menu.html.twig template? When the page is actually rendered, the last suggestion is checked. If it exists, that suggestion is used. Otherwise the next suggestion up is checked, and so on. Of course, if none of the overriding suggestions exist, page.html.twig is the final suggestion. This also explains why page--front.html.twig,
is_front variable is not available in the menu template by default. You can add it there by adding this into your themename.theme file:

function themename_preprocess_menu(&amp;$variables) {
  try {
    $variables['is_front'] = \Drupal::service('path.matcher')-&gt;isFrontPage();
  }
  catch (Exception $e) {
    $variables['is_front'] = FALSE;
  }
}