An EDID emulator like that will bypass the displays internal EDID and report to the PC different resolutions (the ones loaded into the emulator). While the dongle is plugged in, the PC will always see the emulators values, even if your display is turned on.

A few things to think about.

If you change to 1200p instead of 1080p, will the monitor accept that resolution? Many displays will scale different resolutions, so you are probably ok in that it will "work". It depends on the display though. Your display may look worse due to the scaling. Obviously you can just switch back and forth in display setting as needed. Just be aware.

In addition, EDID info has a designated "Preferred" resolution. For example with a 1080p display the 1080p resolution is marked as preferred. When a display is plugged in Windows will usually default to that preferred resolution (on the assumption that is what the display is saying it really wants to use and so Windows should just do that). So with a 4k EDID emulator, when you plug it in, and its not a display Windows has seen before and doesn't know to do any different, Windows may default to outputting 4k. If your 1080p display can not accept 4k, you probably will get 'No signal' or an 'Out of Range' type error. This can be hard to fix because you can't see anything and won't be able to get to display preferences to change to 1200p. So you may need to remote desktop in, or other solution, to change it. I would probably recommend doing the 1200p emulator instead of the 4k one.

This is a great explanation, thanks. They also have a 1200p version of this so I'll try that instead of the 4k one.

I am someone who was interested when I was googling this today. Thank you!

Have you tried setting the monitor to the Steam Deck resolution?

1280x800?

1080p is beyond the display limit of the steam deck

I'm going to try that. Quick question though - could rendering at 1200p on the host and streaming to Deck make the picture look better on the Deck than rendering at 800p?

Hey! Did you ever find a solution for this?

I've ordered the edid emulator with pass through and it's arriving tomorrow so I'll test and post my findings here.