Found a semi-fix / workaround for apps that don't go full screen on the Pixel Fold.
For those who are interested, you can make your own 'app' right from Chrome for almost any website and everyone I've tried opens full screen.
- Open the website in Chrome
- Tap the 3 dot menu in upper right hand corner
- Tap Add to Home Screen
- Name it
- Save
The website will now show as an app on your home screen. Tapping on it will open full screen. Some websites will open in chrome (bummer) but some will open, look and behave just like a normal app in full screen mode.
Try it and see. Twitter is a very good example as it looks just like a full screen app.