Proton fails to initialize optical audio output.

[esiefker]

Not sure if this is a Proton or Pipewire issue, let me know if this is the wrong place. Everything worked previously and I have changed nothing besides regular system updates.

When I start any Proton game with any version of Proton, and my system audio is set to optical stereo output, I get no audio.
I do get a pop-up notification from the mixer

All Linux native software works.
System Wine audio works.
Proton audio works through my G433 headset audio.
Proton audio works through digital output if started with G433 and manually changed to optical stereo output.

If my G433 is connected, but manually set to optical stereo output, and then I run a Proton game, I get audio on the G433 for 1 second and then it switches to optical stereo output.

I can't find any informative log messages. Steam outputs nothing that indicates failure.
Journalctl gives me this:

Oct 11 08:47:34 Iblis pipewire-pulse[2419]: mod.protocol-pulse: client 0x5585ba44bcd0 [voidpyramid.exe]: ERROR command:-1 (invalid) tag:2 error:25 (Input/output error)

Pipewire-pulse works for other software, e.g. mpv.

Proton versions tested:
Proton Experimental
Proton 9.0-3
Proton 8.0-5

Software tested:
Void Pyramid
Sonic Mania
Earth Defense Force 5
Disco Elysium

System is Debian Sid, with Steam from the non-free repository.
x570s motherboard with [AMD] Starship/Matisse HD Audio Controller using Digital Stereo (IEC958) Output.