Does iPad Air 3 have split screen?

Yes, your iPad supports multitasking, Slide Over and Split Screen. Take a look at these Apple video guides:

After viewing, you’ll be ready for the additional Multitasking Guide:

https://support.apple.com/en-us/HT207582

The iPad User Guide for iPadOS is also a rich source of information. Here are links to both the downloadable and online versions of the Guide:

https://help.apple.com/epub/ipad/en/

https://support.apple.com/guide/ipad/welcome/ipados

Split screen is a feature available in iOS 12 or later, regardless of which device you're using.

Here is a support article for more info: https://support.apple.com/guide/ipad/open-two-items-in-split-view-ipad08c9970c/ipados

Make sure that you are are updated to the latest iOS.

Simple answer? Yes!