I have an app where ideally I have sync between web, mobile, and watchos.

Firestore (firebase) works well for sync between web and mobile. But I'm a bit stuck as to the best option for watchOS. WatchOS doesn't support firestore, but even if it does, I think many apple watches don't have internet support so I want an option based on watchconnectivity.

I use watchconnectivity to send the data, but just store it in @State. When I kill the watchOS app, the state goes away, even though I'd rather it persist.

What is the best option to persist it ? Is it CoreData, AppStore, or some other option? CoreData seems like the most reliable option, but also a lot of extra code to keep the watchOS coreData synced with the firestore app. Wanted to post here in case anyone has any insights.

I have some apps on my watch that seem to sync with their iOS companion apps without much problems, even if I turn off the iphone and kill the watchOS app, when I restart the watchOS app, the basic state persists. So these devs are doing something - is it just coredata? appstorage? or something else. Wanted to post here in case any good ideas.