What early tests showed
Chinese tech blogger Wu Xiaojie WJie tested several frequently used apps on the Apple iPhone Duo and Huawei foldables, as reported by Sina. According to gizchina.com, Huawei devices showed apps in multi-column layouts with side-by-side sections, while the iPhone Duo showed many apps in narrow portrait windows at the centre of the 7.6-inch inner display with large empty areas on both sides. The test also found issues with the Dock layout.
According to heise.de, two weeks after launch many of Apple's system apps and popular apps such as WhatsApp, Facebook, Instagram, Overcast and Things had been adapted, while others including Microsoft Teams and many Apple Arcade games still showed large black bars. The outlet said unadapted apps also show a prominent black border on the outer display, and rotating the phone lets them grow somewhat on the inner display.
According to news.qq.com, which cited hands-on checks by creators including He Tongxue, WeChat and QQ initially showed centred layouts with black bars on the inner screen, with around eight in ten common apps not yet optimised at launch. The same report said QQ later issued an update for full-screen adaptation and WeChat released a split-column version that still left a black bar on the right side.
Why apps show black bars on the iPhone Duo
The behaviour depends on which software development kit an app was built with. Apps built with older tools run in a centred window with empty space around them, and developers need newer tools to make them fill the foldable screen.
According to heise.de and gizchina.com, compiling with the iOS 26 SDK produces the black-bar effect, compiling with the iOS 27 SDK is an interim solution that uses most or all of the inner display but not the right-hand status bar area, and compiling with the iOS 27.1 SDK or later lets apps automatically use the full display including the right edge for the tab bar and other icons. Apple made Xcode 27.1 available as a release candidate for submitting updates in early October, but many developers have not yet switched, often because of dependencies on third-party SDKs or analytics and advertising frameworks.
According to gizchina.com, apps built with the iOS 27 SDK can resize to use most of the inner display, while full support including adjusted navigation and interface elements requires the iOS 27.1 SDK. Some developers had added support around launch and several popular apps received updates then, but many apps still need work before the larger display feels consistent.
| Build SDK | How the app appears on the iPhone Duo inner display |
|---|---|
| iOS 26 SDK | Centred narrow window with large black bars on left and right |
| iOS 27 SDK | Uses full inner display size, but does not use the right-hand status bar area |
| iOS 27.1 SDK or later | Automatically uses full display size, including right edge for tab bar and icons |
Huawei wide-screen devices in focus
According to gizchina.com, the Huawei Pura X family includes several formats: the Huawei Pura X with a 6.3-inch inner display and a 3.5-inch outer screen, the larger Huawei Pura X Max with a 7.7-inch inner display and a 5.4-inch cover screen, and the Huawei Pura X View, which is not a foldable but a regular handset with a wide 6.39-inch display in a 16:9.5 aspect ratio closer to a small tablet.
According to PhoneArena, Apple has said the iPhone Duo's inner display offers about 50% more usable surface area than the 6.9-inch display on the Apple iPhone 18 Pro Max, at approximately 175 sq cm versus 117 sq cm. The Duo uses the same 1:1.42 aspect ratio for both its inner and outer displays to allow seamless app transitioning between the two screens, while the iPhone 18 Pro Max uses a taller 1:2.17 aspect ratio.
According to news.qq.com, Huawei's wide foldable was described as using a √2:1 ratio with a 5.4-inch outer screen and 7.7-inch inner screen. The report claimed channel data showed Huawei Pura X Max weekly sales rose 38% in the week the iPhone Duo opened pre-orders from 16 October, with cumulative shipments of the Huawei Pura X series reaching 3.21 million units and shipments for the companion wide non-folding model also reported. GadGeek has not verified those sales figures.
Price and rollout timing
The adaptation issue and SDK requirement apply to the Apple iPhone Duo. The phone went on sale in China on 23 October with a purchase limit of two per person reported by news.qq.com.
According to heise.de, the situation should improve at least in part starting in spring 2027, and according to news.qq.com Apple has set April 2027 as a deadline for mandatory adaptation; India availability and pricing were not detailed in the sources. GadGeek has not used or tested the product.
How to get the improved app layouts
There is no system update that forces all apps to fill the inner display. Users will see wider layouts as developers release new versions built with the iOS 27.1 SDK or later.
To check for those updates, open the App Store, go to Updates and install the latest versions for individual apps, and keep the device software up to date when a new iOS version is offered.
Known issues
Unadapted apps appear as narrow centred windows with black bars on the left and right of the unfolded inner display and with a black border on the outer display, and the Dock layout can also appear incorrect in those cases, as described by gizchina.com and heise.de. The comparison does not assess processor speed, battery life or display quality, and it does not show that every app works perfectly on every Huawei model, only that certain apps made better use of the large screen on Huawei foldables in that test.