I just noticed that the whatsapp web service in my Chrome browser (v85) is showing it's favicon not only in the top of the browser tab (as you'd expect) but also in the actual address bar, to the left of the web address where a padlock icon usually appears.
How is this done ?
I've concluded that this was some kind of odd glitch. I can't now replicate what I saw myself in my own Chrome browser. For now this seems a bit of a mystery.