Is is_front variable available in menu.html.twig template?
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;
  }
}