A hotfix went out for this issue last week. Would take System updates and see if this is resolved. You can alternatively switch your USB port to “XHCI” mode.
I’m looking at this issue now, but in the meanwhile, try this short term workaround:
Cold boot (from shutdown) while docked, or, if you get into this mode, try doing a quick sleep/wake of your device.
Let me know if that does/doesn’t help, and if you still have trouble, please post your display model number, which display connector (and cable, if convenient) you’re using. It helps with reproducing symptoms on my end.
https://help.steampowered.com/en/faqs/view/4C18-08B5-DEC9-3AF4 As another user mentioned, the reset procedure from the support article above is another good thing to try. Since the dock can be powered directly from the Steam Deck itself, if a bad setting or mode gets set, it can be “remembered” even when power cycling with the USB-C power supply. Make sure to unplug Deck + PSU when resetting.
Thanks, will pass this repro on. Very helpful.