Blank Screen(s) when booting or switching to Desktop Mode, while docked and connected to external display

[philfycasual]

Your system information

• Steam client version: 1726683985
• SteamOS version: 3.6.18
• Opted into Steam client beta?: [No]
• Opted into SteamOS beta?: [Yes]
• Have you checked for updates in Settings > System?: [Yes]

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Please describe your issue in as much detail as possible:

Describe what you expected should happen and what did happen.

I expect the external display to show the gaming mode Home screen when first booting. When switching to Desktop mode, the steam deck should be able to load into it successfully, while correctly displaying on both the built-in (if set to be enabled) and external screens.

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What did happen is that the screens remain blank. The hardware appears responsive (haptics are sensed), but the only way out of this is to reboot the deck after disconnecting the display (or turning it off) or undocking the deck. It can also, albeit inconsistently (because the setting appears to occasionally revert to off), be worked around by using the external display safe mode option in the system settings -- though this does not carry over into desktop mode.

If you manage to then boot into desktop mode, workaround or not, both screens remain blank again. In this instance I'm not convinced that the deck actually gets into desktop mode, despite the hardware still feeling responsive. If you hold the power button, unplug things again, then 'turn it on' it will go directly into desktop mode -- as if the device was just woken from sleep.

I can provide further details, e.g. make/model of the monitor, logs if any are required (I don't know the platform well enough to say where or what to look for).

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Steps for reproducing this issue:

1. Dock the deck, make sure external monitor is plugged in (DP) and on
2. turn on the deck
3. Profit??
4. If you've managed to get this far, switch to desktop mode while the above is still true