Mono / .NET based Program crashing, won't start (Noob problem/not bug) #21800

System: Artix Linux (Arch fork)
Mono: Installed package Mono 6.12

This is not a bug, but I'm seeking help as a noob with mono. I downloaded the Linux deb package of dwsim, which is based on .NET and written mostly in C#. I then ran it and got these error messages:

Mono: DllImport unable to load library 'libgtk-x11-2.0.so.0'.
libgtk-x11-2.0.so.0 assembly:<unknown assembly> type:<unknown type> member:(null)
at (wrapper managed-to-native) Gtk.Application.gtk_init_check(int&,intptr&)  (more lines deleted)

I then ran ldconfig:

# ldconfig -p|grep libgtk-x11-2.0.so.0
#libgtk-x11-2.0.so.0 (libc6,x86-64) => /usr/lib/libgtk-x11-2.0.so.0

Gut feel is that I have some config I need to do.

Thanks for your help.