Removing the PSU would quiet things down. The PSU fan though, I had mine break on my computer awhile back and out of laziness and frugality left it for a few months and had no ill effects.

It’s a modified version of Arch Linux.

SteamOS 2 came out almost 10 years ago (!) with the release of Steam Machines in 2015. That one was public but it seems Valve has pulled the links to download it. SteamOS 3 is what is on the Steamdeck which isn’t publicly available yet.