Before I was thinking about creating a binding from the list to the detail. That would work to change the state, but in a real world app we want to save it to an API or data base. I also like having the store as the source of truth. This solution is so simple yet so strong. I really enjoy it. Thanks for answering!

That is interesting. My mind is still tied up with View Models. It makes sense that I pass down the BookStore but still have a @State to handle the UI. I made some tests here and even with TextField this works well when I track the changes and send the updates to the BookStore.