Understanding Xamarin and Xamarin.Forms
To create a mobile app that only needs to run on iPhones, you might choose to build it with either the Objective-C or Swift language and the UIKit libraries using the Xcode development tool.
To create a mobile app that only needs to run on Android phones, you might choose to build it with either the Java or Kotlin language and the Android SDK libraries using the Android Studio development tool.
More Information: In 2020, iPhone and Android have a combined global smartphone market share of 99.6%. What about the other 0.4%? Xamarin supports creating Tizen mobile apps for Samsung devices. You can read about Tizen .NET at the following link: https://docs.microsoft.com/en-us/xamarin/xamarin-forms/platform/other/tizen
But what if you need to create a mobile app that can run on iPhones and Android phones? And what if you only want to create that mobile app once using a programming language and development platform...