aaravchen You could ask around in the GrapheneOS chatrooms, there are some users running GrapheneOS on the Pixel Fold there:
https://grapheneos.org/contact#community
From what I've heard, everything just works. Both the Tablet UI and normal phone UI are fully supported as part of AOSP. The default Keyboard takes up a lot of the screen in dual screen mode, so some users have opted for third-party keyboard apps which have better support for the large screen.