Subscription only makes sense if there’s an ongoing service, e.g. processing in the cloud, cloud data storage, etc.

Apps that don’t need to be subscription:

• Camera apps like Halide or Filmic Pro, wtf
• Any todo / habit apps, the ‘cloud’ part is usually iCloud / Google Drive
• Notetaking apps, e.g. GoodNotes, wtf
• Duolingo, mainly because the contents of some lessons are outdated (missing audio, etc).

why did I misread that as AutoCreamPie?