Ok. Are you using the latest Windows version of Cabbage 2? If not download it from here. You can run it out of the extracted archive if you have Cabbage 1 already installed. Once you open, open your patch and change the CsOptions to this
-d -n -+rtmidi=null -m0d -Q0 --midi-key=4
Then hit Play. Then open a synth, I tested using the hard sync synth from the examples. When this opens hit play. Now launch the Cabbage patcher window. Then patch the MIDI output from your midi instrument to the midi input on the synth. I tested here and we are getting some MIDI being sent to the synth. It’s not as expected, but I think this is just down to some issues with your MIDI instrument. Here’s a screenshot of my setup:
Let me know if this works.