This is what the apple developer website says.
Starting March 2019, all new apps and app updates for iPhone, including universal apps, will need to be built with the iOS 12 SDK and support iPhone XS Max. All new apps and app updates for Apple Watch will need to be built with the watchOS 5 SDK and support Apple Watch Series 4
Does it mean that even the apps already available on Apple App Store needs to be resubmitted with iOS 12 SDK build for it to work on iOS 12 devices starting march 2019?
And what about enterprise apps that are distributed as .ipa files? Will this also need to be rebuilt with iOS 12 SDK for it to work on iOS 12 devices?