What remains in the system after deleting the app: data saved in UserDefaults or in KeyChain?

After deleting the application, data stored in UserDefaults is removed along with the app, as it is stored in the app's container.

Data saved in the Keychain generally remains in the system after the app is deleted. The Keychain is designed for storing sensitive information and can retain data even after the app is removed, unless configured otherwise (for example, using special access attributes). This allows, for instance, saving logins or tokens when reinstalling the app.