Steam Deck Previews Exciting Game Play Upgrades Including HDR And VRR Support
Valve equipped the Steam Deck with a passable LCD screen at 1280 x 800. It doesn't have the color range to display HDR content, but Valve is adding HDR support to the OS. So, you can take advantage of the expanded color gamut if you connect to a compatible external monitor. Likewise, Steam OS 3.5 adds support for variable refresh rates (VRR) when connected to an appropriate screen.
You might notice the built-in display looks a bit different after the update, though. Valve has adjusted the default color rendering to approximate the sRGB color space. That means the LCD might look slightly warmer and more vibrant. There are several other color presets available if that's not to your liking. There are also sliders (see below) for manually adjusting the color vibrance and temperature.

On the functional side, Valve has refined the graphical drivers to increase performance. It specifically made enhancement for Bethesda's newest game, the expansive space RPG Starfield. Performance in Starfield often leaves something to be desired, so every little bit helps. There are also fixes for games like Returnal, Amnesia: The Bunker, and Immortals of Aveum.
The underlying Arch Linux OS has been updated, which will no doubt delight Desktop Mode users. There's a new Plasma desktop interface with widgets, a new windowing system, and better software management. Valve also added a few low-level tweaks to make the firmware reset shortcut more reliable and added optional voltage offset to (potentially) save power. The new update is available to anyone who has opted into the beta channel under Settings > System > System Update Channel.