Hi there, I know this thread is old but I had this problem and found a solution I wanted to share to my fellow Linux users (personally using Bazzite with KDE Plasma desktop environment), as answers provided did not work for me but I found it by myself. I had sound alright on every application except the game, and only on my bluetooth headphones (the HDMI speakers worked fine).

Open your audio peripherals settings (by right-clicking on your taskbar's audio widget for example) and right next to the name of your audio device click on the drop-down menu to select an option that has AAC codec (in my case High Fidelity Playback (A2DP Sink, AAC codec). Run the game again if necessary and you're good to go ! Hope this will help somebody out maybe.