Comment # 12 on bug 1201418 from ted chang

 aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: Generic [HD-Audio Generic], device 3: HDMI 0 [HDMI 0]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 0: Generic [HD-Audio Generic], device 7: HDMI 1 [HDMI 1]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 0: Generic [HD-Audio Generic], device 8: HDMI 2 [HDMI 2]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 0: Generic [HD-Audio Generic], device 9: HDMI 3 [HDMI 3]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
doof@steamdeck:~> uname -a
Linux steamdeck 6.0.0-rc1-1.gc35dc38-default #1 SMP PREEMPT_DYNAMIC Mon Aug 15
00:08:48 UTC 2022 (c35dc38) x86_64 x86_64 x86_64 GNU/Linux

The sound is still not recognized.