About:

@Environment(\.requestReview) private var requestReview

You can refer to this case: @Environment vs @EnvironmentObject.

How do I access EnvironmentValues (RequestReviewAction) in MAUI iOS (formerly Xamarin iOS)?

The more important point is: The iOS18 API for Xcode16 is not currently supported. And you can follow up this issue: [META] Xcode 16.0 Support for .NET 8/9 and MAUI #20802