Changing resolution via Command Preparations only works when Sunshine run in terminal, not via systemd

[FuzzyMistborn]

My main gaming monitor is an ultrawide, so I've been playing with setting the resolution automatically to the client's resolution when I start streaming via Sunshine. However I've run into a problem. When I just run sunshine in the terminal, the following do/undo commands work just fine and the resolution is adjusted as expected.

# Do
sh -c "kscreen-doctor output.DP-2.mode.${SUNSHINE_CLIENT_WIDTH}x${SUNSHINE_CLIENT_HEIGHT}@60"
# Undo
sh -c "kscreen-doctor output.DP-2.mode.3440x1440@144"

However, if I switch to running Sunshine via systemd, it doesn't work, and the following show up in my log:

Jan 06 00:01:13 desktop sunshine[32039]: [2024:01:06:00:01:13]: Info: Executing Do Cmd: [sh -c "kscreen-doctor output.DP-2.mode.${SUNSHINE_CLIENT_WIDTH}x${SUNSHINE_CLIENT_HEIGHT}@60"]
Jan 06 00:01:13 desktop kscreen-doctor[32668]: qt.qpa.xcb: could not connect to display
Jan 06 00:01:13 desktop kscreen-doctor[32668]: qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "" even though it was found.
Jan 06 00:01:13 desktop kscreen-doctor[32668]: This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.
                                               
                                               Available platform plugins are: eglfs, linuxfb, minimal, minimalegl, offscreen, vnc, wayland-egl, wayland, wayland-xcomposite-egl, wayland-xcomposite-glx, xcb.
Jan 06 00:01:13 desktop sunshine[32039]: [2024:01:06:00:01:13]: Error: [sh -c "kscreen-doctor output.DP-2.mode.${SUNSHINE_CLIENT_WIDTH}x${SUNSHINE_CLIENT_HEIGHT}@60"] failed with code [6]

My systemd file is this (pretty sure it's the default but just in case):

[Unit]
Description=Sunshine self-hosted game stream host for Moonlight.
StartLimitIntervalSec=500
StartLimitBurst=5

[Service]
ExecStart=/usr/bin/sunshine
Restart=on-failure
RestartSec=5s

[Install]
WantedBy=default.target

I've looked over the docs a bunch and I'm not seeing anything on point. Am I doing something wrong?

[mickabrig7]

While I don't have an answer to your specific problem, I was able to make your commands work and autostart Sunshine by using KDE's Autostart settings page: