Most of the layouts I've built on macOS are actually simpler than their iOS counterparts because the mode of interaction is so different. Getting data onto the screen in a somewhat natural way is usually less of a contorted process because one doesn't need to deal with a software keyboard, a narrow viewport, lots of scrolling, etc.

The problem with SwiftUI on macOS in my opinion is that it's just not well-suited to the types of layouts common on desktop and especially macOS. It's best at uniform grids and lists which is more of a mobile thing. On macOS you want things like visually balanced whitespace, optical centering of labels+controls in forms, etc which are often rather arbitrary and exactly the thing that SwiftUI is worst at.