Download: P4Merge https://www.perforce.com/downloads/visual-merge-tool and only copy P4Merge to /Applications
from the dmg.
~ $ git config --global diff.tool p4merge
~ $ git config --global difftool.p4merge.path /Applications/p4merge.app/Contents/MacOS/p4merge
~ $ git config --global difftool.prompt false
If you receive the error message: qt.qpa.fonts: Populating font family aliases took N ms. Replace uses of missing font family "Courier" with one that exists to avoid this cost.
run git difftool
and in P4Merge > Preferences... > Text Format > Font
replace "Courier" with "Consolas".
FYI: I don't like using P4Merge as the merge tool, just as the diff tool.