How to download app from iPad to Mac?

I have an often-used app on my iPad Air (iOS 12.4.8) which is no longer in the App Store – which means if I need to reset the iPad for any reason, there's no way to get the app back (since iTunes no longer includes apps in backups). I want to download the app (.ipa file) to my Mac so I have a backup to reinstall if I need it.

I got the iMazing utility, whose web page says "Keep old apps in case they disappear from the App Store. Hang on to a specific version." Only it turns out it doesn't do this, directly contradicting what the web page says. Though iMazing might work to reinstall the app if I can get a copy of it.

Does anybody know how I could get this app (.ipa file) from my iPad to my Mac?

If I jailbreak the iPad, would that make it possible to copy the app (.ipa file)? Never done this, know nothing about it; any suggestions how to learn? I don't want to brick my iPad.