I've opened up a new Beta branch for people who want to help test Controller input and Steamdeck issues.
Right away on the new branch you can find an improved layout for Item Stores on smaller resolutions. There's also an experimental option in the Settings to disable UI scaling and opt for higher res windows. The UI scaling does cause some visual glitches here and there, but nothing major has popped up yet.
Hopefully these additions help some people out while the Steamdeck and Controller implementation is finished fully.