On Mac, if the MIDI input device selected in Preference is not connected, MuseScore hangs any time a UI action is made which would normally produce MIDI output (like when notes are entered or clicked).
- Select a connected MIDI input device in the Preferences under I/O
- quit MuseScore
- turn off or unplug the MIDI device just selected as default
- Restart musescore
- click on a note or add a note <-- MuseScore will hang with a spinning beachball and the only option is to force quit and restart MuseScore.
OS: macOS High Sierra (10.13), Arch.: x86_64, MuseScore version (64-bit): 18.104.22.16871, revision: d2d863f