Remedy is making Codename Condor which is a co-op multiplayer game set in the Control Universe, namely in the Oldest House.
From Remedy’s business review JANUARY–MARCH 2024:
Codename Condor, a part of the Control franchise, moved to full production meaning it has reached the final development stage before a game is launched. Based on wide internal playtests, we can see that the core loop is engaging, and the game brings a unique Remedy angle to the genre.
This is a Bluetooth issue, not Linux or Deck specific. When microphone is enabled on a headset, Bluetooth will switch to a different audio codec. That codec supports one output channel (microphone) and one input channel, so it will be mono audio. The sound quality is good enough for audio calls but not for anything else. The only thing you can do is to disable the microphone. Or, you can do what people have done for couple decades now: complain at Bluetooth Special Interest Group until they improve the standard.