Dynamic volume controls were only introduced with release of iPadOS 15.4 onwards. For reasons known only to Apple, the ability to either enable or disable this feature is not available for the iPad Air5 and iPad mini6.
Use the Home, side, and other buttons on your iPad - Apple Support
Apple invite submission of constructive comments and feature requests via its Product Feedback pages. If you would like to see the ability to disable dynamic volume control functions for your iPad Air5, this would be the most appropriate channel through which to make your voice heard:
Feedback - iPad - Apple