When a view combines .navigationBarBackButtonHidden(true) with a custom ToolbarItem(placement: .navigationBarLeading) back button, both controls render side by side in the navigation bar — the system back button is not fully suppressed, only visually emptied. This appears to be related to the new Liquid Glass toolbar platter system introduced this cycle.
Environment
Xcode 27 beta 3 iOS Version : 27.0 Reproduces on: Simulator 16.0 (1063.4) SimulatorKit 955.7 CoreSimulator 1168
Steps to Reproduce
Create a NavigationStack with a root view and a pushed detail view. On the detail view, set .navigationBarBackButtonHidden(true). Also add a custom back button via .toolbar { ToolbarItem(placement: .navigationBarLeading) { Button { dismiss() } label: { HStack { Image(systemName: "chevron.backward"); Text("Back") } } } }.
Expected Result Only the custom "Back" button (chevron + text) is visible.
Actual Result Two back-button-shaped controls appear side by side: an empty/default system back button platter, and the custom "Back" button.
Confirmed via Xcode's View Debugger (Debug ▸ View Debugging ▸ Capture View Hierarchy): two sibling UIPlatformGlassInteractionView nodes exist under NavigationBarPlatterContainer_v2 ▸ PlatterContainerHostingView. One wraps a bare, unlabeled _UIButtonBarButton (the system-generated back control); the other wraps a BarItemView containing the app's custom Button (chevron + "Back" text). Both are laid out as independent glass platters rather than being merged into one leading toolbar group.
Minimal Reproducible Project Attached: [BackButtonDuplicationRepro.zip] — a stripped-down single-screen repro isolating just this behavior (no navigation stack customization, no third-party code).
Related report This looks like the same underlying issue as thread 812048 ("Toolbar Rendering Bug — ToolbarItem Duplication when Back Button Hidden"), which an Apple DTS engineer has already responded to requesting a reproducible project — hopefully this attached project + View Debugger evidence helps move that along.
Also potentially related: thread 814816 (hidesSharedBackground not working for backBarButtonItem), which points at the same general area of the new Liquid Glass toolbar/platter system.