That's actually what navigation bars looked like back in iOS 12 so maybe your simulator is getting nostalgic.
I also noticed in your sample code you are embedding a NavigationStack inside another which isn't recommended, but that isn't the cause of the problem.
I would definitely file a feedback because there is no reason for the navigation bar to look like that just because of a map somewhere in the view hierarchy.
However, there is some good news… this doesn't seem to be a problem in iOS 26, and most importantly, I have a fix and it's this:
.toolbarBackground(.automatic, for: .navigationBar)
// renamed to toolbarBackgroundVisibility in Xcode 26
What you were seeing was the background of the navigation bar being permanently visible, regardless of the scroll position. It seems like the map sort of forced this behaviour.
Topic:
UI Frameworks
SubTopic:
SwiftUI
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