Volume buttons

There is no user control for dynamic volume on your model of iPad. It is automatic. See this for more information.

Use the Home, side, and other buttons on your iPad - Apple Support

You can always send feedback to Apple about this.

Feedback - iPad - Apple

Dynamic volume controls were introduced with release of iPadOS 15.4 onwards. For reasons known only to Apple, the ability to disable this feature is not available for any new models of iPad and iPad Pro that have since been launched - these models being:

• iPad Air5
• iPad mini6
• fourth generation iPad Pro 11”
• sixth generation iPad Pro 12.9”
• iPad10

This is documented within this recently updated Apple Support document:

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, this would be the most appropriate channel through which to make your voice heard:

Feedback - iPad - Apple