MTR HDMI Ingest Audio plays from both Conferencing and Default device when in call (Lenovo Smarthub)

Paiste the trick in this case would be to mute the default device and use the conference system. If you share content with audio, the audio is part of the content and will be played for the remote party, but also be part of the content shared into the room. So actually the room is not playing your audio ingest, it is playing your content (including the audio).
It would only stop if you don't share the audio into the meeting (making the far end miss it 100%) or turning the volume of the room system down (what will make room participants miss 100% of what the far end says).

So for the sake of meeting equity, share audio into the meeting only and do not use your devices audio at all.