Hey, narocleptic. I'm sorry to hear about the error.
I'm not familiar with Linux at all, so I can't help you resolving this issue (hopefully, our community might have the answer).
However, I do find this discussion in forum manjaro about user having a similar issue in Garry's Mod - maybe this will help? https://forum.manjaro.org/t/libgconf-2-so-4-missing-in-garrys-mod/29114
If not, here's a link to the Web-Browser version of the game. It's basically the same experience as the desktop version, so I highly recommend checking it out in meantime :)