A quick heads up.
Here's a link to a video by Carl Irwin describing how to sync Musescore4 to VLC for writing score to vid.
I've had an enjoyable afternoon setting this up, and testing, and it works well.
Thanks to Carl and the original author of the plugin (L'Moose?) for this opportunity, particularly as the Musescore owners have decided to refuse the pull request for jackmidi to be included in MS4 and later.
Alex.