SwiftUI 4 introduces NavigationSplitView, a component for building sidebar-based navigation on iPad and macOS that gracefully degrades to a NavigationStack on iPhone. The guide walks through creating a basic split view with a sidebar and detail area, fixing a common selection-binding bug by passing a binding to the List, customizing styles (balanced vs. overlay), and applying accent/tint colors independently to sidebar and detail content. Platform differences between iPad and iPhone rendering are also covered, including list style limitations on iPhone.
