Why Store

Depends on the use cases. Please explain more context about when you heard that you should create a Store.

I presume that the "Store" they refer to is in fact the App's Data Model.

SwiftUI apps typically consist of a number of Views (i.e. the User Interface) and a single Data Model ("Store"), which handles all of the data processing logic. The Data Model might also interact with a server, local or external, to store and/or retrieve data. The Data Model is usually a class that adopts the ObservableObject protocol. Properties within the DataModel that change and which the User Interface (SwiftUI View(s)) needs to display, upon change, need a @Published attribute. Then, in the SwiftUI view you can monitor for changes with an @ObservedObject reference to your data model, or to a specific property of it. There are other ways of SwiftUI monitoring for changes.

I also use the Data Model as an interface to an SQLite database, with SwiftUI calling a Data Model function to retrieve data from SQL, format as required, then make the data available to the SwiftUI View e.g. as an array to use in a List. This approach does not rely on monitoring for changes and works best with mostly static data. The function call is made to the Data Model within the List struct and returns the required array.

This Developer reference is useful https://developer.apple.com/documentation/swiftui/managing-model-data-in-your-app

Regards, Michaela