To make a build of a xaramin app for publishing to the iOS store dont you need a Mac at least for one stage? It looks like you do under the "Archive for Publishing" section here:

https://docs.microsoft.com/en-us/xamarin/ios/deploy-test/app...

It's also against ToS to virtualize OSX on non-Mac hardware as far as I know.

I don't think they are just doing that for fun.