[Audio] - Selecting "Speakers" as the preferred "Output Device" overrides the headphone sink fallback.

[ZereoX]

Your system information

• Steam client version (build number or date): 1731433018 (Stable) / 1730253536 (Beta)
• Distribution (e.g. Ubuntu): SteamOS 3.6.20 / 3.7.0 (Deck) and Manjaro w/ Gnome 46 (Desktop)
• Opted into Steam client beta?: Issue is present on both Stable and Beta
• Have you checked for system updates?: Yes
• Steam Logs: steam-logs.tar.gz
• GPU: AMD Van Gogh RDNA 2.0 (Steam Deck) and RX 7800XT (Desktop)

Please describe your issue in as much detail as possible:

If Speakers is explicitly set as the Output Device (instead of Default (Speakers)) prior to connecting a 3.5mm device, audio will continue to playback on the on-board speakers instead of the headphones (ACP/ACP3X/ACP6x Audio Coprocessor Speaker remains the active sink). Switching the Output Device back to Default (Speakers) does allow the device to correctly switch to the headphones sink. This issue is specific to Gaming Mode as in Desktop Mode KDE exposes both devices separately in the audio device tray.

Video

https://github.com/user-attachments/assets/4c69b942-2a14-4062-b565-e20bba5266ea

Steps for reproducing this issue:

1. Navigate to Steam > Settings > Audio > Output Device.
2. Set the option to Speakers.
3. Plug in a 3.5mm device.

Reproduction Rate: 5/5

Affected Platforms

• LCD / Jupiter: Yes
• OLED / Galileo: Yes
• Desktop Deck-like session (gamescope -e -- steam -gamepadui -steamdeck): N/A
• Desktop: N/A

Actual result

• Audio does not switch to the 3.5mm device when connected and playback persists on the on-board speakers.

Expected result

• Audio automatically switched to the 3.5mm device when connected or a separate Headphone option is available when a 3.5mm device is detected. This would allow users to explicitly chose this behaviour if they would like to use an external 3.5mm microphone with the on-board speakers (see video below for example).

https://github.com/user-attachments/assets/c834939e-10cf-408e-9171-6ccb554f3c9c

Notes

• This issue is not present on Desktop as all output devices are exposed separately while on Steam Deck the 3.5mm jack (ACP/ACP3X/ACP6x Audio Coprocessor Headphones) and on-board speakers (ACP/ACP3X/ACP6x Audio Coprocessor Speaker) are both reported under the Speakers entry.
• This issue is not present if Speakers is selected while a 3.5mm device is actively connected.
• When an option is explicitly selected, wpctl status does show them as a Default Configured Devices. Selecting Default (Speakers) removes that setting.

  Settings
  └─ Default Configured Devices:
       0. Audio/Sink    alsa_output.pci-0000_04_00.5-platform-acp5x_mach.0.HiFi__hw_acp5x_1__sink