SteamOS 3.4.11 has been released to the Stable channel for Deck with the following changes:
Firmware 116
- Improved robustness of the Firmware Settings Reset chord (Volume Down + Quick-Access + Power) against some boot hang scenarios.
- Fixed a rare issue that would set the processor TDP limit too low causing CPU and GPU frequencies to be stuck at 400 MHz and 200 MHz respectively.
- Fixed an issue when the charging light would turn back on when plugged in for a while after fully charged.
SteamOS
- Fixed an issue where power button presses could switch games to keyboard/mouse mode.
Firmware updates are not really related to SteamOS updates, Valve just happened to group them.
So you mean that people that are on 3.5 preview will also receive the firmware update because it isn't already in the 3.5?
The beta also had a firmware update included. Don't know if it was the very same or an earlier version.