Chrome – In the new tab “Save As…” disabled in right click menu when displaying generated HTML

In my frontend app I generate the HTML page as string and then open a new tab with JavaScript and write the html to the tab’s document, like so:

const newTab = window.open('about:blank', '', '');
newTab.document.write(this.fullRenderedHTML);

As a result the Save as option in the right click menu is disabled. Is there a way to make it possible for the user to save the page?

I expect the user to be able to save the generated HTML.
Here’s a codepen link to reproduce the issue.
https://codepen.io/socreative/pen/bGJxRLK

Click the Open Tab button then try saving the page in the new tab