Are you sure you're not thinking that Xamarin uses XAML and not WPF? XAML is used by WPF, UWP, & Xamarin Forms, but I don't recall WPF being on anything other than Windows.
Oh, damn, you're right. I only just now realized I've erroneously used those interchangeably for years. /humbly skitter away
Note that XAML is nothing more than a way of serializing object graphs to XML. WPF uses XAML (as do a bunch of others), but the objects created when parsing the XAML can be pretty much anything and all that is not tied to WPF in any way. Case in point: Our main product is a graph display and editing component, using GraphML as its native file format. We serialize visualization and business data attached to the graph as XAML, and while that particular code portion originated in the WPF branch, the format is the same, even in the Java product.