Some of our existing pages use MobX however we decided to stop using MobX for new work for a few good reasons:

1. It forced us to use an experimental language feature (decorators)
2. We went all-in on GraphQL and Apollo to manage our data and local state.

For all the places where we don't store state in Apollo Client, we use plain old React and hooks (useState and useContext). Our first choice in state management it to have all state stored in Apollo keeping local state accurate by using mutation updates, client resolvers, and local cache.