How do I get out of split screen

Key to accessing and controlling (or avoiding) multi-tasking is the small “three-dot” button that is found at the top-centre edge of the visible App windows. 

Information and guidance for using multi-tasking - and Split Screen view - can be found in these support pages:

Use multitasking on your iPad - Apple Support

Close split screen or a floating app on your iPad - Apple Support

The iPad User Guide is a rich source of frequently overlooked information about your iPad and iPadOS. The Guide is available both online using a web browser (such as Safari), or as an Apple Books download:

iPad User Guide - Apple Support

https://books.apple.com/book/id1567104892

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Close split screen or a floating app on your iPad - Apple Support