To complete the MuseScore integration in music21, the following command is sufficient in most cases (it can be executed in an empty Jupyter Notebook page):

configure.run()

If after that the note display in Jupyter/music21 still does not work, open this Notebook.

Here you can directly view and change the path settings for MuseScore within music21.

The usual paths for MuseScore are:

Windows:

C:\Program Files\MuseScore 3\bin\MuseScore3.exe

Mac

/Applications/MuseScore 3.app/Contents/MacOS/mscore

Linux

/usr/bin/musescore3

Attention! If MuseScore cannot be found under this path on Linux, it helps to install MuseScore via apt:

sudo add-apt-repository ppa:mscore-ubuntu/mscore3-stable
sudo apt-get update
sudo apt install musescore3