After selecting the split screen option in the multi-tasking menu, you are returned to your Home Screen to select the app you want to share the screen with. Some apps are not supported, and if selected will simply open in full screen, but VoiceOver gives no indication of which apps are and are not supported.
Open an app which supports multi-tasking, for example Safari.
Go to the status bar and open the multi-tasking menu, and select the Split Screen option.
You will be presented with your Home Screen, from where you select the app you wish to add to a split screen setup.
Some apps are not supported, but you are not warned or prevented from selecting them with VoiceOver.
The new app simply opens in full screen if selected.
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