Xamarin is the lastest C# cross-platform environment for professional app development companies to create an app for iOS, Android & UWP with one shared programming code.
Some older companies are still using native codes for each platform. But all of them are trying to switch to Xamarin. It means, previously if you want to create your app for apple devices like iphone or ipad, you had to hire a mobile app development company to do the iOS app development for you; And for building it on Android devices, you probably need another team or even the same team with a new cost to do the Android app development. But Nowaday the new cross-platform programming is helping us to build an app in a more cost effective way for all platforms and devices.
The main advantage can be seen after publishing the app. When we want to change anything on the app in the future, we do not need to change everything twice or three times on different platforms. So, after-sale support would also be easier for you and us.

So, with Xamarin as a base technology, we are using Unity for 3D games, and firebase for authentication and database management, along with storage management and notification features. We are using different ad networks for different types of apps with hundreds of new features and technologies.
 However we talked about C# Xamarin, we can develop an app in any platform or technology like Python, React Native, Java, Flutter, Swift, Kotlin, and many more.