When I ran git gui, I got this:
git gui
$ git gui git: \'gui\' is not a git command. See \'git --help\'. Did you mean one of these? grep init p
2020
brew install git brew install git-gui git config --global --add alias.gui '!sh -c '/usr/local/opt/git/libexec/git-core/git-gui''
Now, enjoy: