Sunshine doesn't stream Steam Big Picture and streams both Monitors.

Hi everyone, I have been trying to set up Sunshine in my bazzite 40 pc with and RTX 3070 (X11). I have two displays . One through HDMI 1080P and the main one 4K DP. Even though I have changed the display index in sunshine's configuration to the DP one I am only able to stream the HDMI one or both at the same time... But I want only the 4k one. (Resolution in Moonlight client is set to 4k) At the same time, steam Big Picture doesn't open even If I don't have steam opened. I have tried to change the command to steam://open/gamepadui but it doesn't work either. Thanks