I'm currently trying the steam demo, and the linux version appears to be borked, at least on arch linux. I'm not getting anything useful in the terminal, apart from a warning about a potential fork without exec, is there any way I could get some more detailed logs to help you out potentially?
Edit: I can confirm that the linux version above works fine, just the steam demo is borked. Windows/Proton works fine as well, just linux native through steam.