I tell people I don’t use Whatsapp. Which I don’t. It’s obnoxious, and unfortunately very popular. I tell them to use email. Why people would use a proprietary application/platform as opposed to something that is as open as email eludes me. But I suppose convenience trumps everything.
As I understand it, if your number(s) is/are enabled as a Whatsapp number, there is no way to stop people sending you stuff via Whatsapp. So I haven’t enabled mine. I suggest that if you use Whatsapp, keep the number you use with Whatsapp separate from the number(s) you use for regular phone usage.
ADDENDUM: As others have mentioned, you don’t need to keep all correspondence with guests in the Airbnb messaging system. In my opinion, email is the best choice for correspondence in general, because it is easy to archive and search, being text in its natural form. I have all my email since 1996 archived. And if you want to send attachments to the guest, you should do so via email, because the Airbnb obfuscated email system loses attachments some of the time. And their obfuscated email system is best avoided in general, because it messes up the formatting of even plain messages.
But matters directly relating to the reservation are probably best kept in the messaging system (you could duplicate them in email if you want), just in case there are disputes later. And if it looks like you are running into problems, you definitely want to keep correspondence in the messaging system.