How to use split screen on iPad Pro (10.5 iOS 11) in Portrait mode
iPad Pro 10.5-inch, Wi-Fi, Cellular
Hi. As you have shown, you can use Split View in portrait mode, resulting in two narrow columns. iOS is not a windowed operating system, so this split screen effect is quite tricky to implement. It's not just a "tiled" layout.
You can suggest this change to Apple by posting at this link: Feedback - iPad - Apple.
How to use split screen on iPad Pro (10.5 iOS 11) in Portrait mode