I’m working on a moderately complex iOS and macOS app in SwiftUI. I haven’t tried the new stuff yet but it’s definitely a very mixed bag. It can save you a lot of time vs the old APIs for simpler things but it can make hard things even harder.
And you’ll probably find yourself dropping down to UICollectionView and NSCollectionView for performance. Xcode remains a terrible IDE.
AutoLayout is a good example of the last generation of Apple APIs. Even the easy things are painful but if you need to do something really complex there's a way to make it work.
Right now I'm stuck in a situation where any SwiftUI widget except for List has terrible performance but List imposes all these other constraints I can't live with so it looks like once again it's back to UI/NSCollectionView for me.
And you’ll probably find yourself dropping down to UICollectionView and NSCollectionView for performance. Xcode remains a terrible IDE.