Starting in 2013, when I began to work with Xamarin (which was bought by Microsoft in 2016), I designed a ton of macOS application icons. Let me show you the most interesting ones, in chronological order.
Xamarin Studio 6.x icon for the dark macOS system theme. The icon was never officially used by the Cocoa API to switch application icons is not fully supported by Apple and hence very unstable. We decided to use the light version instead.
Visual Studio for Mac (previously Xamarin Studio) remixes the official Visual Studio infinite logo branding, but it still needs to follow Apple Human Interface Guidelines and look native to the Mac platform.