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I would think about where you keep your data, where you keep your business rules and what the handover point is from front end to business rules and data (backend)

When you make the front end as dumb as possible, you will find it easier to switch later.

In stead of focusing on swift you could try a few weeks how far you can get with letting AI build the app for you. For sure you will have to read a lot but as AI can do already so much it will probably be very capable of writing for you the native mobile app.

You could use bubble as a quick mvp builder to better understand what you need and the structure you need.