That google duo doesn't support multiparty conferences in the browser? You can try starting one if you like. They only support 1-to-1 calls in the browser.

It would be a pretty exhaustive list if they stated everything they don't do... As such, I cant give you a link for that.

edit: Here you go https://support.google.com/duo/thread/11344666?hl=en Is that sufficient, or do I really need a reference that something doesnt exist?