Steam Deck no output to Type-c external monitor in Game Mode

[Okoken]

Your system information

• Steam client version: 1704329464
• SteamOS version: 3.5.12
• 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:

In Steam Deck game mode, no output to external monitor when connecting with USB Type-c to USB Type-c cable. Also the Steam Deck internal screen turns black, so probably it recognized the external monitor but somehow failed to output anything. No issue with HDMI cable connection with USB Type-c dock.

Also no issue in Desktop Mode.

Steps for reproducing this issue:

1. Connect to external monitor with USB Type-c to USB Type-c cable, in any time when the Steam Deck is in game mode.

[tygeezy]

I have the same issue with my display.