A question for Apple engineers. Why is it that using a private API (for example, finding the corner radius of a device's screen) can result in the app being rejected for review or even an account being blocked, while using a private compiler API (for example, @_spi) has no consequences?
Private APIs have not been officially released for public use. As such, they are not documented and engineering is not keeping track of them or maintaining them in system software updates. As such, they are subject to change at any time without notice. If you build an app using Private APIs your app may cease functioning, crash, or start operating in unexpected ways at any time.
Disallowing Private API usage in apps available on the App Store is protecting both you and your customers from unexpected inconveniences.
If your app requires functionality that is not provided by public APIs, please consider filing an enhancement request asking for the APIs that you require.