A comparison between Xamarin and .NET MAUI
Xamarin.Forms: Overview
Xamarin.Forms is generally used to develop native cross-platform apps. Basically, Xamarin.Forms is a layer of abstraction that allows interaction of the shared code with the underlying platform code of Android, iOS, and Windows.
Using Xamarin.Forms, a cross-platform mobile app developer can save development time by writing all of their business logic in a single language. Almost 90% of the code required to develop an app is shared across platforms, letting you achieve native performance and the same look on each. .NET MAUI: Overview
As you know, the .NET Multi-platform App UI is popularly known as .NET MAUI. It is used to build native cross-platform apps with .NET for Android, iOS, macOS, and Windows. .NET MAUI is built on top of Xamarin.Forms, evolving the platform to the next level.
With .NET MAUI, Microsoft begins a journey to create a unified .NET platform as a single base class for .NET Core and Mono/Xamarin together.
This is a quite detailed comparison between Xamarin and its evolution, .NET MAUI.