In Xcode 15, run in iOS17, -[NSUserDefaults setObject:forKey:] not work. ***.plist file never be modified
UserDefaults in iOS17 unwork
For many years now, UserDefault has provided no guarantee of where or when it would save its data into the file system.
What are you actually trying to do? If, for example, you're trying to examine existing defaults for debugging purposes, you can use the defaults command line tool in Terminal to inspect the data for your app.