What 3rd party app developers do with their apps is up to them.
Apple has no control over what 3rd party app developers do with their apps or their ability to keep their apps going and updated.
Sorry.
If you just recently upgraded your iPad Mini 3 from iOS 9 or 10, many older apps, that were 32-bit coded apps that have not been updated to 64-bit code for the new 64-bit versions of iOS, like iOS 11, 12 and any other future iOS versions, non-updated apps will no longer work with the newer versions of iOS.
If your iPad Mini 3 was running iOS 10, you should have been getting pop-up window messages from any installed apps that needed updating to 64-bit code and will not work with iOS 11, every time you lauchned these non-updated apps.
No such message would appear if your iPad Mini 3 was still running iOS 9, though, as tbis incompatible app warning was only part of iOS 10.
So, you not have been warned about this.
It would appear the developer of the original Brushes app never intended to update the older Brushes app to 64-bit code status.
The original Brushes app was replaced by the Brushes Redux app back in 2014 and that app was last updated 3 years ago in April 2016.
Brushes Redux appears to be 64-bit compatible.
Brushes Redux by Christoffer Hoel.
https://itunes.apple.com/us/app/brushes-redux/id932089074?mt=8
Perhaps you should have switched over to this version long ago, when you still had the ability to use the older Brushes app and use the iOS 9 share sheet feature to import paintings from the older Brushes app into the newer Brushes Redux app.
It appears the original developer of Brushes app sold off his app and code to another 3rd party and has been resurrected as a new 64-bit Brushes 4 app for iOS 11, and later, by its new 3rd party developer here.
Brushes 4.
https://itunes.apple.com/us/app/brushes/id1168117279?mt=8
Best of Luck to You!
