Ok, I see. I’ll have a read-through that post about how to roll my own Standalone class.
"Let us know why the midi handling of the default standalone target app does not work for you. Maybe we can add it to JUCE"
The app only works with certain devices and as such performs a handshake for before allowing MIDI processing - this involves checking the that input and output for a device can be opened and doing a sysex device enquiry, so it’s not general MIDI handling.