The iPad Air2 is capable of update to iPadOS 15.7.8 - but does not support iPadOS 16.x.
If you wish to use Apps that require iOS/iPadOS16 or later, such as Audible: Audio Entertainment, you have no alternative other than to replace your iPad with a much newer model that supports iPadOS16.
Audible, the App Developer, clearly relies upon functionality that is not available with earlier versions of iOS/iPadOS. If you wish to offer comments or feedback, you should do so to the App Developer - as they have full control of their App's functionality and its development.
How to contact an app developer - Apple Support