I’ve used Arch, Pop_OS for gaming in the past, was looking for a distro that just works and doesn’t have any extra fluff or do anything nonstandard. (For example I don’t like that some programs will only update through the pop shop on pop os and not through the terminal.)
SteamOS is a Debian derivative, and has existed long before the steam Deck was a thing.
Nvm looks like they switched to Arch for v3.