The biggest new features with version 4 are (according to Apple):

- Build iPhone and iPad apps with SwiftUI right on your iPad (requires iPadOS 15.2 or later)

- App Store Connect integration lets you upload your finished app to the App Store

- App Preview shows live updates as you make changes to your app

- Full-screen preview lets you see your app edge-to-edge

- Smart, inline code suggestions help you write code quickly and accurately

- App Projects make it easy to move projects to Xcode and back

- Project-wide search finds results across multiple files

- Snippets Library provides hundreds of SwiftUI controls, symbols, and colors

- Swift Package support lets you include publicly-available code to enhance your apps