I had the exact same Problem.
You need an Android Emulator for your PC, since Whatsapp for desktop always needs to be paired with a phone, then install Whatsapp Business. The Business Version lets you sign up with a landline number. Youll geht a call with the code read to you and youre done.
If you already have a number and are planing to keep it, you can just use that and read the code from your phone.
If you decide to use a desktop app or the web version instead, you will have to open Whatsapp on your phone once every two weeks or it will unpair.
Even this hand picked example is wrong as it returns true if num is 1