(Moonlight & Sunshine) All Games & Windows on Primary Display instead of Steam Deck

Hey everyone!

I’ve been using my Steam Deck to stream games via Moonlight and Sunshine from my Windows 11 PC (RTX 4090) without any issues—until I got a new monitor (ASUS ROG PG32UCDM).

Here’s the problem:

I can connect from my Steam Deck just fine using Moonlight, and everything seems to work. I’m using a virtual display driver and have Sunshine configured correctly. However, whenever I connect, my Steam Deck gets treated as the extended monitor and the main display is not inactive.

Even if my main monitor is off, all open windows (including Steam, Games etc.) stay on the powered-off main screen. If I drag a window to my Steam Deck and launch a game, it still opens on the main monitor instead of my Steam Deck.

I’ve already set Sunshine to auto-display on the Steam Deck (IDD Display 5) when streaming starts, but Windows still defaults to the main monitor, even when it’s off.

Before I could just start up my PC, leave the main monitor off. Connect through my steam deck, type in my password and launch steam. All games we're automatically set to the correct resolution etc.

Has anyone run into this issue before or knows how to force Windows to treat the Steam Deck as the primary display when streaming? Any help would be super appreciated!

Thanks in advance! 🙏