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 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 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.

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

Steam Deck works just fine, so I guess the Machine will too.