When using KMM Kotlin Multiplatform Mobile, do I get a real native UI for Android and iOS, that looks the same like when using e.g. directly Jetpack Compose on Android? With all the effects, e.g. when touching a button? Or is it a just half "native" UI like on React Native?
Kotlin Multiplatform mobile helps you to build a common business logic and has nothing to do with the UI. This means that the app's UI is written with the standard techniques that the single platform allows, for instance Jetpack Compose (or Android Views) on Android and Swift UI (or UIKit) on iOS.
In terms of project setup you will use Android Studio to write the shared common logic and to write the Composable functions for the Android App UI. Conversely, you need to use XCode to write the iOS App's UI.