It's a good thing Microsoft doesn't think that way. It apparently has metrics that show desktop development is not stagnating, but rising thanks in part to Windows desktop OS usage also rising [1]. See its plans for WinUI v3 [2]. WinUI is not cross-platform but it is talking about it.

[1] Comments from Ryan at MS https://www.dotnetrocks.com/?show=1660

[2] https://github.com/microsoft/microsoft-ui-xaml/blob/master/d...