Wow. I assumed you could use Whatsapp on the web but you literally can't. You have to have an Android or Iphone. I guess maybe there's a way to fake it with emulators on your computer but that's a lot of work that you shouldn't need to have to do.
WhatsApp accounts are directly tied to a single phone number, both for user discovery (that way, you can simply message everybody in your contacts who has the app - just the way user expect it to work) and for spam prevention.
Creating a smartphone messaging app without this feature would be orders of magnitude more difficult, you simply can't get normie users to go around "hey, what's your WhatsApp user name?"
I think there’s also an unofficial Python library, so you can write a simple script that keeps your account active (and use the web client).
It's still Android. How do I do it on a GNU/Linux phone?