Add the raw JSON to the end of your Postman Visualizer template.

rawjson.js

let template = `
<script src="https://cdn.jsdelivr.net/gh/google/code-prettify@master/loader/run_prettify.js?autoload=true&amp;skin=sunburst&amp;lang=js" defer></script>
<!-- Your content goes here -->
    <hr>
<h1>Raw JSON Response</h1>
<pre class="prettyprint">{{raw}}</pre>
</div>
`

pm.visualizer.set(template, {
    response: pm.response.json(),
    raw: JSON.stringify(pm.response.json(), null, '\t')
});