No external sound output on Steam Deck gamemode when connect to external monitor with certain resolution settings

[KrisCris]

Your system information

• Steam client version: 1737601106
• SteamOS version: 3.6.21
• Opted into Steam client beta?: Yes
• Opted into SteamOS beta?: Yes
• Have you checked for updates in Settings > System?: Yes

Please describe your issue in as much detail as possible:

When the Deck is connected to an external monitor, and set to a certain resolution, i.e. 1280x800, the external audio via HDMI doesn't work.
This only happens in the game mode, desktop mode is not affected.

Steps for reproducing this issue:

1. Connect to external display
2. Set resolution to 1280*800
3. Changing the audio device doesn't work.