SteamOS 3.5 has just been released to the Preview channel, and includes new features that are still being tested. You can opt into this in Settings > System > System Update Channel. Display The default color rendering for Steam Deck has been adjusted to emulate the sRGB color gamut, resulting in a s...
So it's being worked on, and it seems all involved are trying to get it right - it sounds like gamescope on SteamOS doesn't need to worry about solving all the problems that general purpose desktop compositors will have to.
Why exactly is Linux having so much trouble with HDR?
macOS handles it trivially, Windows screws up color mapping but supports HDR fully, iOS handles it perfectly, Android relies on apps reporting HDR correctly but also works.
Desktop Linux is just now getting it's first HDR supported system, and it's the Steam Deck - why? It's HDR, not quantum computing, what's wrong in the chain?
Desktop Linux had been a bit behind the others on display features due to the legacy of X. As everybody moves more to Wayland that better enables these sorts of things, they're catching up.
If only AMD would catch up with raytracing, DLSS, compute, and HDMI 2.1...
Everytime I think about switching to AMD these things always hold me back. There isn't a solution where you can throw money at the problem, unfortunately.
DLSS is proprietary NVidia technology. That's just like blaming Nvidia not being able to catch up on CPUs because Intel and AMD did not give them a license for the x86_64 instruction set. AMD supports the other technologies just fine.