alt Hacker NewsSwift is a cross-platform compiled programming language that offers memory safety as a tentpole feature.
SwiftUI is a platform specific API for developers who are writing native apps for that platform.
You can think of Swift as being similar in concept to Rust and SwiftUI as being similar in concept to Win32.
SwiftUI is also now an API for writing Android native apps, too.
I don't know why you skipped over that part? It's maybe like when Google rewrote Java. Win32 is a bad comparison because there's no Win32-compatible API for native apps on other platforms (that I know of?) except for emulation, but the Android SwiftUI project is not using emulation, it runs the code natively and the result is native Android UI.