Click on the MIDI din plug icon in the mixer strip for any MIDI track. This will turn off MIDI input for that track. MIDI is different from audio and so the process for handling things isn’t 100% identical.
MIDI does not playback during recording (no internal monitoring in Ardour)
MIDI plays back after the recording
Your instructions (if I followed them correctly), give me 2 and 3, but not 1. Is it possible to turn of MIDI monitoring so that it behaves the same way as turning off audio monitoring in Ardour?