I sold my mini 4 for a mini 5
I have the ottterbox defended mini 4 case.
Despite the camera and volume buttons being slightly off, it still fits and works. No issues pushing the buttons and the camera isn't blocked.
The problem then was the microphone. It's in the middle on the mini 5.
The defender 5 had a hole where the microphone is. So a power drill later and my otterbox defender mini 4 case now works with the microphone.