How to detect if a new user was created?

MongoDB Atlas App Services & Realm
1

I would like to copy data from the local realm to the synced realm only if the logged in user was just created.

struct MainScreen: View {    
    @EnvironmentObject var app : RealmSwift.App
    @ObservedResults(Item.self) var items

    var body: some View {
        NavigationStack {
            
        }
        .onAppear {
            // move local to sync
            if let localRealm = try? Realm(), let user = app.currentUser {
                if items.count == 0 { // if user.isNew
                    let localItems = localRealm.objects(Item.self)
                    for item in localItems {
                        // local -> synced
                        let syncedItem = Item(value: item)
                        syncedItem.userId = user.id
                        $items.append(syncedItem)
                        // delete local
                        try? localRealm.write {
                            localRealm.delete(item)
                        }
                    }
                }
            }
        }
    }
}

Is there a way to tell if a user logged in for the first time?