Update at 20:10 UTC: this Beta seems to have a pretty major bug. I would suggest you stay away from it for now otherwise you might find you can't open things on Linux and Steam Deck.
Valve has released a new Steam Client Beta for both desktop and Steam Deck, with new fixes and some new features too like showing full or partial controller icons when hovering over items.
- Changing download regions no longer requires restarting the Steam client
- Show icons for partial and full controller support in Library when a game portrait is focused or hovered
- Add a rollup of gifts received in the Quick Access > Notifications area
- Controller configurator now groups commands if they are attached to the same input
- Controller configuration browsing screen can now preview configurations and the selection processes now previews then applies instead of directly selecting the configuration
- Fixed some errors causing the Library not to render properly
- Fix the "Start in Big Picture Mode" setting not updating
- Center the navigation column in the Big Picture Overlay vertically to match the rest of the main menu
- Standalone keyboard can now be brought up outside of Big Picture Mode
- Fixed some issues using the Paste button outside of a web context
An important detail they seem to have left out though, is that this new full / partial controller icon that appears when you hover over a game in your library is not actually on Steam Deck. It appears to only work on a desktop PC in the New Big Picture Mode (it doesn't even appear on Steam Deck Desktop Mode with New Big Picture either). This is the second time they've noted something not actually there for the Steam Deck, like the last Beta mentioning new controller options for idle turn off time and turn it off when exiting Big Picture. Seems they once again copy and pasted bits of the changelog, without enabling it on Steam Deck directly.
Here's how it looks on Desktop Steam: