There are various ways to store persistent data within your app.
Your app can store a user's settings in various ways. For each usecase, there's a best practice.
Most likely, you'll want to store settings per-device.
Most app-specific settings can be stored and retrieved through ManagerSettings. This enabled your app to save and retrieve any value that is JSON-serializable. App Settings are saved across app restarts, and are only deleted when your app is uninstalled.
For non-JSON serializable data, e.g. binary files, the
/userdata/folder is writable on Homey Pro.