The top distro is SteamOS, which is based on Arch, but does not appear as such in the stats. The Arch appearing in the stats has to be CachyOS and other gaming-distros, as also real Arch-users.

But yes, SteamOS makes ~25% of the users. Though, thinking about, do they collect per account, or per device? I do have a Steamdeck, but mainly play on the big desktop running on debian, so I'm curious if I'm appearing as one or two entries in that stat.