Echoing that I also ran into the same issue, but refunded it on Steam because of it because I was still in the refund window. Really would like a response to this, and/or the linux build added to steam.
I actuality managed to get it to work, if you still care. Still waiting for ProtonDB to approve my report, but it involved installing a non-standard Proton version via Protonup-qt, nothing more.
