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 slightly warmer and more vibrant color appearance. Added Settings -> Adjust Display Colors, to tune the display's Color Vibrancy and Color Temperature.
HDR can now be enabled in Display Settings if supported by the external display.
VRR can now be enabled in Display Settings if supported by the USB-C adapter.
Excited for these two.