I have exactly the same issue, started occurring with Xcode 12.5 / iOS 14.5. Only on iPadOS, not using StackNavigationViewStyle (I want two columns) and with 5 NavigationLinks in the same view.
Interesting (for me at least) it seems the first time a link is triggered the destination view is presented correctly, but subsequent triggers fail.
This happens for me as well. I hope this can be fixed relatively quickly.