Finished App Architecture by the objc.io team. The patterns hold up — MVC, view models, and the testing discipline around them — and the real-world case studies are the reason to read it over a blog post. The caveat: it predates SwiftUI and Combine, so everything is UIKit and storyboards, and applying any of it to an existing codebase is far harder than the clean-slate examples suggest. Still the book I’d hand a beginner who wants to structure an app properly.