.NET Maui is the evolution of Xamarin. There is a lot to be excited about with .NET Maui. While this is still early days with .NET Maui and I have not yet had time to evaluate the Mobile.BuildTools with .NET Maui, there is also no reason why the Mobile.BuildTools would not work with .NET Maui. Many of the features included with the Mobile.BuildTools such as the Secrets API, is completely cross platform and can be used with literally any C# project including AspNetCore, Unit Tests, etc.
For Platform Specific functionality such as the Image or Manifest processing, these rely on the iOS/Android SDK's which are shared by traditional Xamarin applications and .NET Maui apps. As such these should continue to work. If you encounter any issue with the Mobile.BuildTools and a .NET Maui application please be sure to file and issue on GitHub.