

SteamOS is immutable, and has its own updater because of it. While SteamOS is related to Arch Linux, it is far from the same distro.
Regular Arch Linux can install local packages, the process is described on the Arch wiki. SteamOS has no built in mechanism to update without an internet connection, and installing packages manually is not recommended (due to the immutable nature of the system).
In order to update SteamOS from a local file, you would need to figure out how SteamOS updates work, and somehow trick the Steam Deck into accepting your local images. This is far outside the scope of anything related to Arch Linux, and not very well documented. The better option is to update your Steam Deck by connecting it to the internet.
Also of note, the latest version of SteamOS (as far as I’m aware) does not have any significant changes when it comes to controlling the fan speed.
Keyguard, which works on Bitwarden-compatible servers like Vaultwarden