I don't use Steam, but nonetheless I've tried with several versions of GE-Proton to no avail. :(
Thanks for your help, anyway. :)
Sure enough!
This is the log I get when I try to run the game: https://pastebin.com/i32SLZV1
At first I thought the relevant error was the inability to find the libnode.so library, so I tried again but this time pre-loading it: https://pastebin.com/TMfKPy5v
No complaints about it this time but it still crashes, so the culprit is probably the font-related error.
I'm on Arch Linux with the KDE desktop (hence the KWallet and KLauncher errors in the logs), dunno if the Desktop Environment could have any influence...