u/24_Charles

These are settings I tried, works for me when playing HDR games on steam. I don't know if others would like to give it a try and see if it still works. Rendering API works differently.

################
### MONITORS ###
################

#LG C3 TV
monitorv2 {
output = HDMI-A-2
mode = 3840x2160@120.00Hz
disabled = true
scale = 2
bitdepth = 10
vrr = 1
cm = hdredid
supports_wide_color = 1
supports_hdr = 1
sdr_min_luminance = 0.005
sdr_max_luminance = 80
min_luminance = 0
max_luminance = 4000
max_avg_luminance = 300
}

experimental:xx_color_management_v4 = true
render:cm_enabled = true
render:cm_fs_passthrough = 0 # Set to 1 when playing DirectX 12 games in HDR.
render:cm_auto_hdr = 2
debug:full_cm_proto = true

# for cm = hdredid or edid ; hdr or sdr pretty much
# Vulkan Rendering API Steam       # DXVK_HDR=1 ENABLE_HDR_WSI=1 gamescope --hdr-enabled --force-grab-cursor --mangoapp -w 3840 -h 2160 -r 240 -f -O HDMI-A-2 -- %command%
# DirectX 12 Rendering API Steam   # PROTON_ENABLE_WAYLAND=1 PROTON_ENABLE_HDR=1 gamescope --force-grab-cursor --mangoapp -w 3840 -h 2160 -r 240 -f -O HDMI-A-2 -- %command%