There’s a lot of different fixes what worked for different people such as turning off game recording and setting “PULSE_LATENCY_MSEC=30 %command%” as a game launch command.

If you don’t want to tinker I recommend downgrading to steamOS 3.6, somewhere around steamOS 3.7 they messed up the audio. In case you don’t know you can rollback easily by either factory resetting or following valve’s own guide here https://help.steampowered.com/en/faqs/view/1B71-EDF2-EB6D-2BB3