I honestly don't think it's legal to use the name WhatsApp unless you propose a service totally different (If you sell chocolates and are called WhatsApp, there

I honestly don't think it's legal to use the name WhatsApp unless you propose a service totally different (If you sell chocolates and are called WhatsApp, there would not be any problem for example). Writing "Unofficial" or "desktop" won't change the fact that you propose the same service and using their name to promote it.