Doesn't WhatsApp still use a keep alive connection to your phone in order to display chat on your computer?
It was this very reason I never started using this app.
I stumbled upon this when working from a cafe and the 2019 MacBook Pro battery went from 100% to 2% in under 2 hours. When I checked Activity Monitor's Energy tab, WhatsApp was by far the largest consumer of energy, despite me doing absolutely nothing in that application (not receiving a single message during that time).