unfortunately not giving a good test result

Yeah, the browser must first support WebRTC before you can use it with BigBlueButton (or any other WebRTC-based application).
That's not accurate. I don't know what's up with that test.webrtc output (might be related to connectivity and/or permission and/or a bug with the test tool itself), but Yandex is a Chromium-based browser and WebRTC works just fine with it.
The problem here is that we don't have an Yandex entry in the minBrowserVersions config in settings.yml by default, so the browser will only get the legacy client. If that is set up, Yandex will work just fine.