IANA considers .tw to be "Taiwan, Province of China", as does that ISO link. As I understand, China pretty much bullied everyone else into not recognizing Taiwan so the rest of the world (like the UN) agrees Taiwan isn't a country. That's why one reason Microsoft asks for your Region, not country.

There appear to be other ccTLDs like .IO and .AQ that aren't countries. (Probably more.)

And I'm just being pedantic.