I have tried an Omec Teleport and Bheringer as input. Both load fine: I can see them in as input and output in the ‘Interface’ section. But I am getting no signal in, or out, in the standalone version (I can’t see midi notes being generated or hear anything).
Midi Guitar works fine as a plug-in in Logic.
I installed the latest 2.2.1 Catalina version of Midi Guitar. Running on OSX Catalina.