Is it possible to Target, Build and Run an iOS SwiftUI App from inside of a Swift Package SDK?

No. There is no such thing as an application target, and SwiftPM is ignorant of entitlements, code signing, and just about everything that goes in Info.plist. I usually extract all code except @main extension MyApp {} into a SwiftPM library, along with any resources the system does not need to be able to find in the main bundle. But that is as close as you can get.