Depends on what you mean by offline, but we're able to interact with UI and trigger mutations while offline, and it will replay the graphql calls in correct order once online again.
With Firestore, even when offline you still see your edits in your query results (flagged as such). This cannot be done with GraphQL, as the meaning of a GraphQL mutation is arbitrary, so the client can't change the offline query results accordingly.
If the interface is graphql, you should be able to use Apollo Client[0] which has offline support.
[0] https://www.apollographql.com/docs/react/