The PlatformIconKind is specific to the target platform.
The icon kind defines various meta information about the icon slot such as the required layer count. Specific icon kinds can be found in platform extension namespaces. Currently only iOS, Android and AppleTV support icon kinds, which can be found in:
UnityEditor.Android.AndroidPlatformIconKind
UnityEditor.iOS.iOSPlatformIconKind
UnityEditor.AppleTV.AppleTVPlatformIconKind