Well I have bad news for you.
https://bugs.kde.org/show_bug.cgi?id=491411
Overriding the EDID is easy but ATM the driver disables VRR if you override it under wayland… at least it does on my case, 3090 , HDMI 2.1 , LG C1
here is my service:
/etc/systemd/system/edid.service
[Unit]
Description=EDID Override Service
Before=sddm.service
RequiresMountsFor=/usr/lib/firmware/edid/lg.bin
[Service]
Type=oneshot
ExecStart=/bin/sh -c ‘for edid_path in /sys/kernel/debug/dri/*/HDMI-A-1/edid_override; do if [ -f “$edid_path” ]; then cat /usr/lib/firmware/edid/lg.bin > “$edid_path”; fi; done’
RemainAfterExit=true
[Install]
WantedBy=multi-user.target