This beta update doesn’t change much, but the name of the update makes me think Valve is nearly ready to push 3.6 to stable.
The biggest changes I know of are things like it using ZRAM instead of swap for dealing with high memory conditions (games like GoW will no longer crash the deck due to a memory leak using all the system’s ram/vram/swap), and a revamped update system that makes system updates faster and more reliable. There are several major improvements that happened on the steam client side of things (like toggling what bluetooth LE devices wake the deck, quick BT connect menu in the QAM menu, etc) that may or may not have made it to stable already. There are a lot of bug fixes of course, many things complained about in the recent bug discussion thread have been fixed in 3.6.
Overall there’s a lot less major features that come to mind than with the 3.5 update, but I’m also probably skipping over a lot of stuff.