folks,
for anyone trying to get HDR through moonlight on steamdeck oled screen: you can’t yet (option to toggle it will be greyed out whatever you try). this is due to vulkan rendering not being implemented.
dev is aware and working on it as confirmed here: https://github.com/moonlight-stream/moonlight-qt/issues/1117#issuecomment-1818441950
timeline not known, so just make it your wish for the upcoming holidays and we might get it :)