I'm developing for a 27 inch iMac and having the exact same problem as you. The problem is obvious: the entire UI operates on just one thread AND re-renders stuff that hasn't been updated. There's no way to know when the rendering has finished and there's no way to separate areas within the UI to render independently. SwiftUI is nothing more than a failed proof of concept and Apple never respond when they know its their fault. I've found it hard enough learning Swift and SwiftUI, so I don't want start learning an about to be depreciated UIKit. So come on dear Apple, give us something that JUST WORKS. Perhaps I should have chosen Python. Certainly the networking would have been easier!

By WE, I presume you mean iOS developers. Perhaps you are unaware that serious apps need to be written for macOS, where there is often a need for pre and post UI processing. For this, a viewModel is the only sensible option.

I needed to click UPDATE on the Xcode 13 page in the App Store. Maybe this was because the server was very busy at that time. Anyway, 13.2.1 is working now.

@Jason why don't you take it off the App Store until its working? Or does TODAY + ETA? + Fixed = NEVER ?

I think I was taken in by Apple's marketing. In fact, it's not the only problem. I've discovered many things that don't work on macOS.

I tried to tick your answer, but I accidentally ticked my own. Sorry.

Thank you and I'm sure you're right, so I'm about to try out workingdogintokyo's suggestion.

This looks very interesting - including how you use environment. My app is ambitious for a novice and I'm very slow. It has 8 Toggles with more to follow, so it will probably take me quite some time to try this out, but I will come back and let you know how it went. Thank you workingdogintokyo for responding with such detail.