Firefox has supported stereo opus for a very long time (four years at least?). We know it works, it's used by medical professionals for their job and they wrote a message a few month thanking us for this feature, that doesn't seem to work on other browser (according to them, but I see tickets open on chromium).

Of course all the chain has to be stereo, that goes without saying: input signal is stereo, negotiation has been done in stereo, having enough bandwidth is important (otherwise opus goes mono), and then playback has to be on stereo hardware (but that's the easy part).