As Dror Mikdash mentioned below for macOS, you do not need to downgrade VirtualBox to 6.0.x any more.
In fact, doing so “broke” an existing VirtualBox VM - I think because 6.0 conflicts with Windows Subsystem for Linux. Uninstalling WSL resolved the conflict - but was probably unnecessary if I had just stayed with 6.1 in the first place!
Also, when adding “C:\MinGW\msys\1.0\bin” to your PATH variable, place it on a separate line.
rsync did not work with it appended to PATH with a semicolon as show in the lecture notes.
Hope that helps.