The controversy became particularly heated after reports suggested platforms like SteamOS could still fall under the law due to their ties to proprietary application ecosystems.

Ehhh. I think that'd be a hard argument to make. I mean, the OS is open-source. You can download it and modify it and reinstall it or whatever. Sure, it runs Steam, which is proprietary, but so does any other GNU/Linux distro.

https://en.wikipedia.org/wiki/SteamOS

The core operating system is free and open-source software, while the Steam client remains proprietary.

Like, the only way in which SteamOS differs from another Linux distro is that Valve, which makes the proprietary client, also happens to be distributing the OS.