(Ubuntu 18.04 LTS) Could not load file or assembly 'netstandard, Version=2.0.0.0

Welcome to the forum @geee1w

Supported by this forum post and a 2013 decision from the mono devs, still with an open issue on

Please see if following the installation directions provides you with assemblies reported as missing.
Attempting to trace with dpkg and apt series of tools gave a clearer answer for mono than graphics.