Yeah it's the de facto communication method for personal communication. I have never worked at a company where people use WhatsApp to communicate. It's always Slack or Teams or Mattermost.
Heh. I have a friend here in the US. His father passed away in his home country. No will. The whole family needed to show up in court for probate, but he could not travel at that time.
The court: "No problem, just join the session on video using WhatsApp"
In Brazil even subpoenas can be sent via WhatsApp.