iPhone Duo Split View: why some apps still show black bars around them
If an app looks boxed in with black borders when you open it next to another app, this is why — and which apps have already fixed it.
Split View is fixed at 50/50
iPhone Duo's inner display supports Split View, letting you run two apps side by side. Unlike iPad multitasking, the divider between the two apps is fixed — you cannot drag it to give one app more space than the other. Every app gets exactly half the inner display, full stop.
Why some apps do not fill their half
The black bars appear when an app has not been rebuilt with the iOS 27.1 SDK. Apple has been clear that existing apps continue to work on iPhone Duo without any changes required — they simply run in a compatibility mode that treats the available space like a fixed-size window, similar to how an old iPhone app looks letterboxed on a newer, larger iPhone screen. The app is not broken, it just is not aware of exactly how much space it actually has, so it renders at a fixed size and leaves black space around itself to compensate.
Apps updated for iOS 27.1 use size classes instead of fixed dimensions or orientation checks, adopt system containers like NavigationSplitView and TabView that automatically adapt to the available space, and handle the asymmetric safe areas created by the fold and camera. Once an app does that, it fills its half of Split View completely.
Which apps have already fixed this
Apple has publicly confirmed three third-party apps as optimized for iPhone Duo at launch: Netflix, Zoom, and Slack. All three have adopted the new SDK ahead of the October 23 launch, so they should fill their half of Split View rather than appearing boxed in.
Beyond those three, Apple has not published a comprehensive list, and most developers are still working with iOS 27.1 tooling that only recently became available — so expect the list of optimized apps to grow steadily after launch rather than to be complete on day one.
What this means if you pre-order
If an app you rely on daily has not been updated, it will still work on iPhone Duo, it will just look boxed in with black bars around it in Split View until its developer ships an update. That is worth checking for any app you consider essential before you decide how much the Split View experience matters to your decision to pre-order.
We will keep our apps directory updated as more developers confirm iPhone Duo support after launch.
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Spotted something to fix, or an app we should cover?
This article is independent research, cross-checked against Apple's developer documentation. If something's out of date, or you know an app that deserves a look, let us know — and if you're building for iPhone Duo yourself, we're happy to talk.
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