How to get data folder for defunct app from iPhone 12 to mac?

Hello and thank you to anybody that can help solve this problem.

My wife for years used this app called Stigma to keep a journal/diary.

Just recently, her iPhone 12 was acting up so I did a full restore. Problem is after all the apps loaded, the Stigma app had one of those 'download arrows' through the icon. I pushed it and was told it's no longer in the store. Since Apple long ago stopped allowing us to save the actual apps in a backup, I see no way to get the app back as the company no longer exists.

However, since the app was not deleted, the data folder is still there with at least a couple hundred mb of info in it. I have scoured the internet to figure out how to access this folder/d-l the data but all I could come up with was the app needed to have file sharing on and then Mac apps such as AnyTrans (the one I have) can access these files. Of course Stigma did not come up in the listing of apps we could access.

So now I need some tech genius to tell me how get to these files and d/l them to the mac. I don't even know if the data is encrypted but I at least need to exhaust all possibilities. I've recovered files from blown hard drives like this and it was possible to force textedit to open them and we were able to recover plain text (which is ALL we want to do to reconstruct here diaries)

Please help. My wife is really saddened that this happened. I blame myself because I forgot about the 'forced update' on all the apps and did not try and backup her data (if Stigma even allowed that)

Thanks again for any input/help.

Mike C.