As reported in FB25363417:
A UIKit based app running on macOS 27.2 (or macOS 27.0.1) via Mac Catalyst no longer has functioning state restoration. Upon app restart, there is no NSUserActivity being provided to the scene in the UISceneDelegate method scene(_:willConnectTo:options:).
This can be tested with Apple’s own sample app “Restoring your app’s state”. Just update the sample project with support for a Mac Catalyst build. Using Xcode 27.2 on a Mac with macOS 27.0 or 27.2, build and run the Mac Catalyst version of the app. The main screen appears with a list of products. Select any product so you see details of the product. Quit the app. Run the app again. Note that you are not returned to the previously selected product detail screen. Instead, you just see the main list of products. If you run the same app and perform the same steps on a Mac running macOS 26.x, then when the app is restarted, you correctly get returned to the previously selected product detail screen.
The problem is being caused by no NSUserActivity being passed into the scene delegate on app startup. While running the app on a Mac with macOS 27.x, put a breakpoint on the initial guard statement in scene(_:willConnectTo:options:) and you will see there is no activity on app restart.
This is impacting paid customers of my existing app since upgrading to macOS 27. They no longer get returned to the app’s previous state when restarting the app.
It is expected that state restoration should work on macOS 27 just as well as it does under macOS 26 in an app built with Mac Catalyst.