NET MAUI is built bottom-up, and each layer provides APIs used to build the APIs in the layer above. The bottom layer is the platforms themselves (Android, iOS, macOS, and Windows). The next layer is the .NET run time for each platform (WinRT on Windows, Mono on everything else) built on the platforms' APIs. Above this is the .NET Base Class Library (BCL), and built upon that is the .NET abstraction of each platform's APIs available for use in .NET apps. For example, .NT for Android contains .NET abstractions of Android's APIs, usually consumed in Java or Kotlin. The .NET MAUI API is a cross-platform layer that you can use to write apps that will run on any of the supported platforms, and Handlers map the cross-platform controls and APIs to their platform-specific counterparts at build time. Meanwhile, your code is written top-down; you write a .NET MAUI app, and the architecture takes care of encapsulating it for lower layers.
