hi

If you are experiencing any difficulty with third-party apps then please contact the app developer directly --> How to contact an app developer - Apple Support

Ask the App developer to release the app for lower iOS versions also.

If the app developed has abandoned the app, there's nothing we as only users can do for you. And Apple doesn't have access to the data in a 3rd party app, so Apple can't help you. You need to reach out to the developer if possible and seek assistance from them.

This is why I NEVER trust important data exclusively to a 3rd party app. For things dear to me, like photos, I make sure I have alternate backups in other places so I can never lose precious memories.

update your phone to IOS 14, this should fix issues.