[borland]

There's more to an app than just the UI layer; Catalyst helps with not only the UIKit parts, but other surrounding stuff like app launching, integration with system features (sharing etc) which differ between mac/iPhone, and other things like that.

It holds value even if you wrote all your UI in SwiftUI. Whether it's a dead-end technology or not, only apple knows (and they won't tell us), but SwiftUI alone doesn't remove the need for it.