This is the best summary I could come up with:
Valve has now released the latest SteamOS 3.5.1 Preview for download, fixing up some more issues in the Steam Deck OS like the backlight staying on when docked.
Fixed a case where an SD card with filesystem errors would be mounted as read-only.
Fixed internal display rotation being erroneously reported to the game.
Fixed a long-standing issue where the internal display backlight would always stay on.
Fixed bug with HDR applications showing in wrong colorspace if they moved their window during swapchain creation.
Fixed a bug where switching to the Plasma Desktop transition could result in broken colors.
The original article contains 207 words, the summary contains 98 words. Saved 53%. I'm a bot and I'm open source!
This summary (and sadly, also the GoL title) has somewhat buried the lede here: The firmware update that comes with 3.5.1 Preview adds undervolting controls — with the obvious implications of improving the battery life.