If you install Xamarin function in the vs installer, it will install mono framework. please see this document:https://learn.microsoft.com/en-us/xamarin/get-started/what-is-xamarin#xamarinandroid
Xamarin.Android applications run within the Mono execution environment, side by side with the Android Runtime (ART) virtual machine. Xamarin provides .NET bindings to the Android.* and Java.* namespaces. >The Mono execution environment calls into these namespaces via Managed Callable Wrappers (MCW) and provides Android Callable Wrappers (ACW) to the ART, allowing both environments to invoke code in >each other.