Mac gaming would have been light years ahead of where we currently are if Apple officially supported Vulkan. I believe early versions of Proton targeted both Linux and MacOS. But Valve walked away after Apple showed little to no interest in working with them.

They stopped the flash sales after they implemented their refund policy.

I don’t have an Nvidia card myself but have you tried the latest Wine-GE through Heroic?

Worst case, you can pick up the native Linux version on Steam right now for 80% off.

The original SteamOS was based on Debian. But that’s been unmaintained for years. Don’t use it.

SteamOS 3.5 is currently available for the Steam Deck only and is based on Arch Linux. Valve plans on generally releasing it but they haven’t yet.

The latest Debian or Ubuntu should work fine.