How can I load the mobile or desktop versions of websites?

Some websites decide whether to serve a mobile or desktop version of their site based on the browser's User-Agent string, which is an HTTP header that identifies the browser and device. By default, 3D WebView uses the browser engine's default User-Agent. However, you can force 3D WebView to use a desktop or mobile User-Agent by calling Web.SetUserAgent(), like this:

void Awake() {
  // Use a desktop User-Agent in order to load the
  // desktop versions of websites.
  Web.SetUserAgent(false);
}

If you use this approach and it still seems like the wrong version of the site is being loaded, then it's likely that the website styles itself as mobile or desktop based on the width of the webview rather than based on the User-Agent header. You can increase or decrease the width of the webview to match a mobile or desktop browser by adjusting its resolution like described in this article.