Technically, steamOS because it’s designed to play games and it’s what the steam deck uses. That probably won’t have many other non-gaming features though, and I’ve personally never used it. In my experience, you can get most games without a hyper-aggressive anti cheat working on any Linux distro with varying degrees of effort, just a matter of having all the needed libraries installed! The more popular distros like Ubuntu, popOS, Fedora, even Arch (btw) should have a lot of helpful information out there on how to get Lutris or Steam set up.

I can’t argue with @Ashelyn@lemmy.blahaj.zone 's answer of "SteamOS running on the Steam Deck. Beyond that, on normal x86 gaming PC hardware? There isn’t a meaningful answer. I have perfectly good luck gaming on Linux Mint. Others prefer Arch or its forks, some prefer Nobara which is on the Fedora family tree.

What’s the best distro for gaming on Linux? The one that you keep installed.

Personally, I’ve been gaming on Arch with minimal issues for 2 years. Mostly stick to steam games for the low effort required though.