This will be a quick one, but I’ve been having this long term issue with Steam Remote Play on both my Steam Deck & Apple TV. When I launch a game with remote play, I get no desktop audio and Steam is monitoring my Microphone input as if it was my desktop audio.
I recently installed OBS and ran into the same issue, so I decided to look into it. The culprit was Easy Effects.
If you have Easy Effects installed, Open “Preferences” and then un-check “Process All Input Streams”. After a reboot & changing OBS to “Default” on the desktop audio monitor my sound issues were fixed.