Just download the disk image from the WhatsApp website and drag the app to your Apps folder. When multi-device support finally does come to the public beta, WhatsApp users will be able to sign in to their account without needing to first login on their iPhone. The macOS public beta includes improved voice note recording support, but doesn’t yet have the promised multi-device feature. There’s also confirmation in the WhatsApp iPhone app code that a native iPad version is finally on the way.
The private messaging app WhatsApp is now available as a public beta for macOS with features not yet available in the regular public release.