How can I downgrade my ipad mini 4

Downgrade from what - a beta release, or something else?

If you are currently enrolled in a beta programme and wish to return to using the current production version, this support page provides the necessary information to remove the beta from your iPad:

How to uninstall iOS beta software - Apple Support

Other than being able to restore the most recent “production” version of iPadOS, with very limited exception, it is not possible to restore an earlier version of iOS/iPadOS. All versions are digitally signed by Apple; only the most recent release can be installed as signing certificates are revoked soon after release of a more recent version.

Sorry, downgrade from iPadOS 14.7.1 to an earlier version of iPadOS is not possible. iPadOS 14.8 is current.

If you are having difficulties with an App following a system software update, you would be best advised to contact the App Developer:

How to contact an app developer - Apple Support