The update to SteamOS 3.8.14 for the Steam Deck has been released for all users.
It fixes an issue where WiFi would be limited to lower speeds on certain routers that advertise incorrect MCS requirements, along with general security and stability improvements.
SteamOS 3.8.14 has just been released for all users with the following changes:
General
- Fixed an issue where WiFi would be limited to lower speeds on certain routers that advertise incorrect MCS requirements
- Security and stability improvements

Source: Steam