<wx-open-launch-weapp
          style="height: 90px;width: 100%;"
          id="launch-btn"
          username="gh_9a674dd"
          path="/pages/index/index.html"
          @error="handleErrorFn"
        >
        <script type="text/wxtag-template">
            <style>.btn { padding: 12px }</style>
            <button class="btn">打开小程序</button>
        </script>
      </wx-open-launch-weapp>

https://developers.weixin.qq.com/doc/offiaccount/OA_Web_Apps/Wechat_Open_Tag.html