Both the Preview and Beta Steam deck channels just got a great bunch of quality-of-life improvements, including the new Steam Desktop Client, check out the changes below:
Added a new warning icon to the header that will display when Steam Deck can't reach the Steam servers. Clicking the icon will navigate a page with more details.
The wifi icon will no longer show a yellow exclamation mark when Steam Deck can't reach the Steam servers. It will still show this icon if Steam Deck can't reach the internet (e.g. the connection has a login portal).
Added support for Mouse4 (Back) as B button in the interface
Fixed opening the "Reorder controllers" dialog in the main Big Picture Window when a game is running
Added a new config export path that works while offline. In the personal configuration dropdown, the options are now "New Personal Save", which is this new option and "New Sharable Personal Save", which uses the existing Steam Workshop backend.
Filter the configuration export options based on whether the device is connected to Steam/Offline
Fixed some flashes when adjusting sliders in the Quick Settings section of the configurator
Fixed moving right in the mode settings page not jumping to the appropriate settings sub-page
Fixed turning off the Dual Sense Edge controller
Overhaul of the In-Game Overlay, with an updated design and new features
New Notes app, saved per game, and accessible in-game or out
Steam Client notifications are now richer and more useful
The screenshot manager has been completely refreshed with new functionality
Full desktop mode changes can be seen here
You can see the full release info here also here.