Re: I'm puzzled...
In fairness, WhatsApp Web is an absolute shit-head for browser blocking in general - it's not just Vivaldi that gets impacted.
I've had it block Chromium, and just occasionally decide the Firefox on Linux can fuck off too.
I tend to just have UA switcher tell it I'm on Safari on Mac now, and everything works fine. In fact, I think WhatsApp Web was my first experience of being blocked based on UA in nearly a decade
Icon because the WhatsApp developers have gimped their own product