I have found that for Lilypond, MacPorts is the only reliable way to get a new version on newer macOS builds.
I have my MacPorts install working happily alongside my homebrew install, with default settings for both.
Once you get MacPorts installed, lilypond is as simple as
sudo port install lilypond
If you have any trouble installing it, i.e. a conflict ...
Answer: There is no way to force stems to automatically only go one way in GP7.
Workaround: You can manually change stem direction. You will avoid giving yourself a headache if you either do this all at the end of in batches, rather than as you're writing, because it can be a very tedious process and really only serves an aesthetic purpose (as pointed out ...