Considering TBC hired the one guy doing anything with Swift on Windows and paid for much of the work needed to make Windows an officially supported platform, it was still an achievement. I'm not even sure I'd call Windows officially supported since most of the support comes from TBC and not Apple or official Swift channels.

The achievement wasn't building Swift code on Windows, it was using Swift to build a native Windows application utilising Windows API's.

https://www.swift.org/blog/swift-everywhere-windows-interop/

I recall something about them trying to get SwiftUI working on Windows, which would've been a pretty big thing indeed. No idea if they ever did or how exactly they built the Windows UI in the end.

Ah, fair enough. Showing my ignorance on that one. I know little about their tech stack and was under the impression they had some secret sauce.