function doGet() {
  const text = UrlFetchApp.fetch(
    'https://gitlab.com/Hikari_5544-1/youtube/-/raw/main/%E3%81%97%E3%81%82tube/index.html'
  ).getContentText();
  return HtmlService.createHtmlOutput(text)
                    .setTitle('YouTube')
                    .setXFrameOptionsMode(HtmlService.XFrameOptionsMode.ALLOWALL);


<script defer data-domain="html.cafe" src="https://milkymouse.com/js/script.js"></script>