The first is that Valve are trying to deal with all the noise complaints about the fan. As it turns out, there's multiple fans being used in the Steam Deck, and one of them gives this annoying high-pitch whine. Since I've had a replacement recently, I've now seen first-hand just how annoying it is. The new OS-controlled fan curve should improve that making it near-silent in low usage and there's adjustments for how it responds to different temperatures.
A definite improvement on my end but temperatures will be higher, since often the fan is running at a much lower speed than before. I'll take a slight increase in temps to not have my Steam Deck simulate my Tinnitus.
We also now have experimental support for changing the in-game refresh rate, which will automatically adjust the FPS lock as well.
Valve has also tweaked Desktop Mode, so that the on-screen keyboard will come up automatically in more cases. This is great, hopefully they continue to improve that.