Using 2012 Mac running High Sierra (MacOS 10.13)
Using Korg X5D feeding through a Roland UM-One Mk MIDI-USB converter.
Various tests have confirmed that MIDI signals are passing both ways from computer to the keyboard and back.
In Notion, however, there is no information going in either direction:
* MIDI keyboard doesn't produce notation in Notion
* playing scores (that have been entered using the onboard keyboard in Notion) produce no sound on either internal speakers or connected external outputs