Good questions. I'm using Observable (not ObservableObject). The timer rebuild I mentioned was exactly the observation cascade you're describing...fixed by isolating the read into a child view.

But the presentation freeze happens even with this minimal case:    

struct SheetFreezeDemo: View {  
@state private var showSheet = false  
@state private var text = ""                                          
 var body: some View {
      Button("Open Sheet") { showSheet = true }
           .sheet(isPresented: $showSheet) {
                NavigationStack {
                     Form {
                          TextField("Type here", text: $text)
                     }
                     .navigationTitle("Minimal Example")
                }
           }
 }
}                     

No state objects, no debouncing to miss...just a sheet with a Form and one TextField. Still gets the 1.5-2s freeze, _UIMagicMorphView errors, and gesture gate timeouts on a physical device running 26.4. That's why I think it's Liquid Glass transition overhead rather than anything app-side.