I believe this means because people can run iOS apps on a Mac (even though it was built for iOS), once you actually make a real macOS app, that the “iOS version” is no longer available on the Mac.
So like I have an app that’s iOS / iPadOS only. But people with M1 chips (silicon Macs) can run my iOS app on their Mac.
When you make the real macOS app, people could no longer run the iOS version, on their Mac