Here's a better version I modifyed

<script>
    function openGame() {
        var win = window.open(url, '_blank', 'fullscreen=yes');
        var url = "https://link/"
        var iframe = win.document.createElement('iframe')
        iframe.style.width = "100%";
        iframe.style.height = "100%";
        iframe.style.border = "none";
        iframe.src = url
        win.document.body.appendChild(iframe)
    }