> then you're not living in a country where the vast majority of communications are done on WhatsApp or Signal

I live in the USA and use Signal for, like, 3 friends that I also can call or text, and I've never used WhatsApp in my life.

So, if you live in the USA, you can absolutely get by without those two.

But there are likely other apps that would be more difficult to do without. Not impossible, mind you, just more effort.