Answer
MAUI is the successor to Xamarin.Forms. Key differences: MAUI uses a single project with multi-targeting instead of one project per platform; it uses a new handler-based architecture instead of renderers; it ships as part of the .NET SDK workload rather than a NuGet package; and it adds first-class desktop support (WinUI 3 and Mac Catalyst).
Real-world example A team migrating a Xamarin.Forms app consolidates five platform projects into one MAUI project, dropping custom renderers in favor of lighter-weight handlers.