GrapheneOS runs on an extremely limited set of hardware, mostly Google's own Pixel phones.

There's a shot of GrapheneOS on a tablet just past the three-minute mark in this video. I suspect that's a Pixel tablet (of which thee are several), though I'm not certain and the video doesn't specify:

<https://redirect.invidious.io/watch?v=aNgupWEV13M&t=188>]

Google Pixel tablet: <https://store.google.com/us/product/pixel_tablet?hl=en-US>

Discussion on Reddit says Google Pixel and Pixel Fold are both supported (tablets): <https://old.reddit.com/r/GrapheneOS/comments/16bp6e9/anyone_...>.