These problems appear solved on iOS 18.5 GA.
Building with Xcode 16.3 on macOS 15.5 GA and running live on iOS 18.5 GA:
No more duplication of toolbar items( the NavigationStack wrapper workaround is no longer needed)
The Toolbar now correctly adopts name of the file you open each time
Of course I'll be retesting as soon as Xcode 16.4 is available with an iOS 18.5 simulator.
This is a huge relief as these problems started with iOS 18.0 and have been blocking me from adopting DocumentLaunchScene and converting 100% to SwiftUI.
I've not used the "prepare document closure" so cannot comment - sorry.
Topic:
UI Frameworks
SubTopic:
SwiftUI