So I compiled the app using the latest XCode, now when I run it, even on older OSX versions, it works as expected. This means that developing with SwiftUI, the behavior you get isn't tied to the OSX, it's tied to the compiler !!! That is unexpected, and honestly, kind of unbelievable.

The ScenePhase only seems to update on the last document opened, so it doesn't work properly. The only way I could make this work was by checking if the url passed in contains "com.apple.documentVersions". Kind of a hack, but it is the only thing that seemed to work reliably. Hopefully someone else has a better solution.

Not sure if this is correct, but the browse previous versions has the scene phase as background, and I can inspect this and create an alternate UI.

Sorry Apple for my delay in responding. I did not have notifications turned on. I do not have any 3rd party crash library in use - and certainly not linked. I incorrectly marked the answer as accepted. This is still an issue I'd like to understand.

Understood. I see the same behavior with Pages. I guess I'll need to add an 'Export To' instead. Thanks for your help.

Thank you for your help! Is there anyway, to have that menu option permanently available? (It is a very common operation in this app, and my original AppKit native version worked this way - this is my first SwiftUI app). The Save panel does not appear when I press Save - it does when I use Save As. It appears to be using "auto save" (I have another ticket asking how to disable this).

Did you every figure this out? Apple support is painful - I guess the only way to get a response is to file developer bug tickets.

It is crazy that you can't at a crash even figure out the element that SwiftUI was trying to render... I am having a similar issue when using 'delete' in List of a ForEach - the SwiftUI framework is calling back into my collection using an index - but the index doesn't exist because it was deleted. It shouldn't be using the index anyway - as the backing data structure is Indentifiable and Hashable.