I don't want to sound negative, that's all nice and good, but since it's about the "Microsoft" (=online) and not Windows (=local) account (although I think they

I don't want to sound negative, that's all nice and good, but since it's about the "Microsoft" (=online) and not Windows (=local) account (although I think they try to blur the line pushing the former in all possible ways), it shouldn't matter what language it's written in - it could be just web page embedded in any widget. And from this point of view, it makes sense to use a web-related framework - not because of it being cross-platform (kind of, I believe only Windows and macOS are supported, for Linux you need something like Proton).