MIDI works from time to time
USB MIDI is not well handled if ever.
It is some kind of misunderstanding, to get it working it helps (sometimes) to start Synthesia and then restart Mosescore.
On the other hand there is never any problem with MIDI in Synthesia.
Of course Musescore is great but with so bad MIDI support it looses so much.
Comments
Whatever MIDI device you use, it needs to be connected and switched on before you start MuseScore. Or you need to toggle the MIDI button (that 5-pin DIN connector icon in the toolbar), off and back on. Or use Edit > Preferences > I/O > Restart Audio and MIDI devices (which is the same thing)