Has anyone tried the new HDR option in SteamOS 3.5 on this external OLED screen?

Here, when I enable it, everything becomes much too gray, almost as if this HDR mode disables the OLED functionality of the screen!

I notice that the screen correctly detects the mode because the HDR indicator appears in its overlay, and I also see that this HDR mode disables all the screen’s preset profiles.

I’m not sure if this is normal or if the HDR mode is experimental and buggy?

I’ve tried changing various Steam display settings in HDR mode, but without success.