I have multiple document based SwiftUI apps without any NavigationBar customization. Since upgrading to iOS 26 , when these apps launch, sometimes their navigation bar icons appear grey (as if only the button shadows were showing) and the document title is white, so it’s invisible.
One of the apps has an Inspector: here, whenever the Inspector appears, the colors are correct.
This behavior has been consistent since the first iOS 26 developer beta and can be reproduced on iOS 26.1 beta 23B5064e.
So far I have only managed to reproduce this in light mode.
Are you able to reproduce the issue using the Building a document-based app with SwiftUI sample code ? If you are, please open a bug report and post the FB number here once you do. Bug Reporting: How and Why? has tips on creating your bug report.