I've uploaded the Linux build!
But there are a couple caveats.
Namely, there's an issue with AMD GPUs that breaks certain critical shaders which unfortunately renders the game unplayable. It may be possible that the proprietary AMD drivers work correctly, since so far I've only received reports from players using the open source ones. NVIDIA users are unaffected so far. I haven't received any reports from users running on Intel integrated graphics.
It's unlikely that I can fix this during the crowdfunding period, since I don't have access to an AMD/Linux system to test on. But I plan on putting one together after collecting funding from the KS. Just need make make sure that succeeds ;)
While we're only planning to officially support Ubuntu-LTS for logistical (and sanity) reasons, I haven't received any complaints of distro-specific issues yet... although I'm sure they exist if you go obscure enough.
At the moment the main difference with the Windows build is that animations during the research presentation screen don't play, and a static image is displayed instead. This is only a temporary solution.
The other difference is that Unity doesn't support the IL2CPP scripting backend for Linux yet, so we're using the somewhat slower Mono backend until that changes.
Lastly, I've received nothing but glowing reports from users who have tried running the game on Proton. Although, it's worth reading these steps to resolve a particularly silly path issue that Steam/Proton have with certain non-steam games.