SwiftUI is not usable yet on the Mac. I can't talk about its state on iOS, but on the Mac you will run into deal breaking limitations even for the most basic apps.
If you want to make Mac apps, learn AppKit. You can use AppKit from Swift just fine, there's no need to use Objective C. Some of the text APIs are a bit cumbersome to use with Swift because of the different string semantics, but for the most part writing AppKit code in Swift is pretty sweet.
If you want to make Mac apps, learn AppKit. You can use AppKit from Swift just fine, there's no need to use Objective C. Some of the text APIs are a bit cumbersome to use with Swift because of the different string semantics, but for the most part writing AppKit code in Swift is pretty sweet.