Seems to region locked. There isn't a word about the game being given away, unless I log out of my account and use a VPN.
What even is the point of region-locking a fucking giveaway?
Edit: well, at least changing the region in the settings works. I guess it defaults to whatever country it thinks the IP the account was registered from belongs to?
SteamOS also uses an immutable filesystem and the system updates as a whole. Because of that, there is no risk of something updating separately and breaking compatibility.
It's fairly common for things to update on regular linux distros and break e.g. anticheat support in Proton or some other thing.
Another thing SteamOS does, at least on the Steam Desk, is actually using two partitions. The updates are always installed to the inactive one, so there's always one image that's known to work. Even if an update fails, the device will simply boot into the intact OS image. Regular distros usually don't have much in terms of fail-safes, so if things break, they have to be fixed manually.
Basically, SteamOS is trying to be as reliable and "hands-off" of an OS as possible to provide best console-like experience.