Thanks for the suggestion. We tried setBackIndicatorImage on every route that should cover it, and the iPhone Duo vertical bar behaves differently from the top navigation bar: UINavigationBarAppearance.setBackIndicatorImage(_:transitionMaskImage:) on UINavigationBar.standardAppearance (and compactAppearance, scrollEdgeAppearance, compactScrollEdgeAppearance), on the page's UINavigationItem, via UINavigationBar.appearance(), and via the legacy backIndicatorImage / backIndicatorTransitionMaskImage. In the top navigation bar the marker image appears in every case. In the Duo vertical bar, the system back button always shows the system chevron (‹). The marker is ignored. Control: a leftBarButtonItem set to UIBarButtonItem(image:style:target:action:) does show the marker in the vertical bar, with the default axisBehavior. Questions: Is it expected that the system back button in the vertical bar ignores backIndicatorImage? If so, is there a documented way to change its icon there? For a custom back control we use a leading image item, which does move into the vertical bar. In our tests a leading item disables the interactive pop gesture. Is there a supported way to keep swipe-back with a leading item on the vertical bar?

back-indicator-nav-vs-vertical-bar.png