We think we have a patch that enables this on the gamescope side but could use extra eyes - this will be of interest to anyone working on Remote Play, particularly for Steam Machines https://github.com/ValveSoftware/gamescope/issues/2126#issuecomment-4938319735
PipeWire 1.6 and newer finally provides support for BT2020/ST2084 video capture/streaming. This should allow Steam's PipeWire desktop capture backend to support HDR video data from Linux hosts.
The catch is that this also needs to be exposed by the compositor, and because 1.6 is new this is still in progress: