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.
Alan Wake’s American Nightmare. Just finished the story mode. It’s Steam Deck Verified, so it runs and plays well, and it’s easy to play with a controller because it has a bit of auto-aim/aim correction.
I did enjoy it. Not a must play by any means, but it does add to the lore of the Alan Wake series. If you are a fan of that game series, I recommend playing this. And if you aren’t, you probably should play the other games in the series. 😉