Removed the outdated libraries from the lib folder in the game directory, and installed the equivalent system libraries to get it to run on Arch. Needs to be started manually from the terminal to work.

These are the library files I left in the lib folder, but your mileage my vary:

libavformat-ffmpeg.so.56
libavutil-ffmpeg.so.54
libbluray.so.1
libcrystalhd.so.3
libfmodevent64-4.44.61.so
libfmodex64-4.44.61.so
libicudata.so.56
libicui18n.so.56
libicuuc.so.56
libopenjpeg.so.5
libQt5Core.so.5
libQt5DBus.so.5
libQt5Gui.so.5
libQt5OpenGL.so.5
libQt5Widgets.so.5
libQt5X11Extras.so.5
libQt5XcbQpa.so.5
libQtSolutions_PropertyBrowser-head.so.1
libschroedinger-1.0.so.0
libssh-gcrypt.so.4
libsteam_api.so
libswresample-ffmpeg.so.1
libswscale-ffmpeg.so.3
libva.so.1
libvpx.so.3
libwayland-client.so.0
libwayland-cursor.so.0
libwayland-egl.so.1
libwebp.so.5
libx264.so.148
libx265.so.79```

Does not launch when using the default Steam native install, starts using the latest Proton version but crashes when starting a local multiplayer game. Removing old libraries and replacing then with up-to-date equivalents was the only way I got the native version to work perfectly on my Arch system.