v1/vendor/chi-teck/drupal-code-generator/templates/hook/themes_uninstalled.twig

/**
 * Implements hook_themes_uninstalled().
 */
function {{ machine_name }}_themes_uninstalled(array $themes) {
  // Remove some state entries depending on the theme.
  foreach ($themes as $theme) {
    \Drupal::state()->delete('example.' . $theme);
  }
}