The irony there is that the Steam Machine can't actually run the full Steam library since most games aren't made for Linux. Most run on it via Proton, many even run well, but it is very far from "all the games play without issues".
Can you imagine if the PlayStation Store sold games on the PS5 that you couldn't play there because they were actually Windows games?
Steam clearly shows a badge showing if it runs on Linux. You can filter out stuff that won’t run.
Just filter out: Fortnite, Roblox, GTA Online, Call of Duty, Destiny, Valorant, PUBG, etc...
It isn't a short list of AAA games that don't run on SteamOS.
There's no game worth installing a rootkit for. The market is far more diverse and interesting than the handful of popular AAA titles , most of which are just shooters
There is a certain group of gamers who care about all of those games, but there is a not insignificant group who doesn't at all. So while it's not a non issue, it's not a show stopper that you can't play online shooter games. And that really is the only genre of game that won't work. Everything else has been flawless on linux.
Since it's not locked down I assume you could install windows on it
you don't even have to, you can do a single GPU passthrough to VM and integrate it seamlessly.
Steam Deck works just fine, so I guess the Machine will too.