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"
It sounds like the court they are referring to is in the "home country". The friend whose father passed is in the US but the "home country" is where the father passed.
In Brazil even subpoenas can be sent via WhatsApp.