I made a LilyPond 2.19.84 installer for use on MacOS 10.15 from MacPorts lilypond-devel, available on the link below. It installs in /opt/lilypond/, with the program in /opt/lilypond/bin/lilypond.
If you have already something installed in this directory, it may be prudent to remove it first. This can be done by the command sudo rm -r /opt/lilypond https://web2.storegate.com/share/JPhrvtH
