Okay here’s what I stumbled through.

This is on a fedora server machine with an intel ARC B580. I intentionally chose fedora because my fedora skills are ass and I wanted to improve them so…

1. enable rpmfusion repos - go here (https://docs.fedoraproject.org/en-US/quick-docs/rpmfusion-setup/) make sure to include nonfree. we need the intel-media-driver from there. The one included in the fedora repos is incomplete and generally wont be enough for what we want.
2. enable the copr repo for sunshine - at this time, there isnt anything in stable for fedora 43, so we enable the beta repo with “sudo dnf copr enable lizardbyte/beta”
3. install the packages - run “sudo dnf install intel-media-driver sway seatd nano pipewire wireplumber Sunshine”
4. open ports on the fedora firewall - I’m a hack and used cockpit for this. log into the cockpit UI and got to Networking->edit rules and zones->add services. add TCP 47990, 47984, 47989, 48010 and UDP 47998-48000
5. add a sunshine user on the machine - run “sudo adduser sunshine -m”
6. set a password for the sunshine user - run “sudo passwd sunshine”
7. add sunshine user to the required groups - run “sudo usermod -aG video,render,seat,input sunshine”
8. enable seatd at boot so the sunshine user can create a headless wayland session in the background without having to be logged in - run “sudo systemctl enable --now seatd”
9. enable linger so things can run by themselves as that user - run “sudo loginctl enable-linger sunshine”
10. create config directories - log in as the sunshine user we created. run “mkdir -p ~/.config/sway ~/.config/sunshine ~/.config/systemd/user”
11. create sway config - run “nano ~/.config/sway/config” and ensure the following is included in the file:

output HEADLESS-1 {
pos 0,0
mode 3840x2160@60hz
}
exec swaymsg create_output HEADLESS-1

default_border none
default_floating_border none

12. create the initial sunshine config - run “nano ~/.config/sunshine/sunshine.config” and ensure the following is included in the file:

capture = wlr
encoder = vaapi

13. config systemd to launch sway at boot - run “nano ~/.config/systemd/user/sway.service” and make the file look like this:

[Unit]
Description=Sway Wayland compositor
Documentation=man:sway(5)
After=pipewire.socket wireplumber.service
Wants=pipewire.socket wireplumber.service

[Service]
ExecStart=/usr/bin/sway
Restart=on-failure
RestartSec=2
Environment=XDG_SESSION_TYPE=wayland
Environment=LIBSEAT_BACKEND=seatd
Environment=XDG_CURRENT_DESKTOP=sway

[Install]
WantedBy=default.target

14. config systemd to launch sunshine at boot (the way we want it to) - run “EDITOR=nano systemctl --user edit sunshine” and put the following in the area that will apply the override:

[Unit]
After=sway.service
Requires=sway.service

[Service]
Environment=WAYLAND_DISPLAY=wayland-1
Environment=XDG_SESSION_TYPE=wayland

[Install]
WantedBy=default.target

15. enable the systemd services - run “systemctl --user daemon-reload” then run “systemctl --user enable --now sway” and “systemctl --user enable --now sunshine”
16. configure sway to change resolution to whatever the moonlight client asks for - access the sunshine webUI by pointing a web browser to https://(your server IP):47990/ and go to the applications tab. in each entry you want to assign this ability to, hit edit and add the following DO command sh -c "swaymsg output HEADLESS-1 pos 0 0 res \"${SUNSHINE_CLIENT_WIDTH}x${SUNSHINE_CLIENT_HEIGHT}@${SUNSHINE_CLIENT_FPS}Hz\"" and if you want an undo command set it to "sh -c swaymsg output HEADLESS-1 pos 0 0 res 3840x2160@60Hz"

There, you now have a headless, resolution-matching, zero-copy, lightweight sunshine install and you didn’t need any dummy plugs, connected monitors, EDID injection, etc.

There are likely things I missed but this is what I’ve got so far.

I have this setup with Plasma, and it is probably easier to do this at the Linux level. I added this to my kernel command line: drm.edid_firmware=DP-1:edid/lg-ultra.bin video=DP-1:3840x2160@60e

Where that EDID file I dumped from a spare monitor using a method I got here.

Anyway, it can be tricky to pick the right device, but I can confirm Sunshine sees it and works properly, and it can be managed like a normal monitor.