He! I didn’t install it as far as I can remember. Too long ago. It was just «there». It could be envoked in a terminal just by typing emacs. I didn’t think much about it. Now after I unfortunately switched to Catalina it isn’t no more «there». And it seems like all my funny elisp stuff is gone too. I tried to compile the latest version but there’s no autoconf on the Mac. I tried to install a binary but this causes some trouble with Apple‘s security policy. Years ago I played around with homebrew my PATH was cluttered somehow. I supressed the ugly details and decided to never use it again. And unfortunately it seems like the disk with my TimeMachine Backup got lost during my move to my new house.
Not that it helps with the underlying problem at all, but I've always ignored the OS' copy and installed my own from homebrew. (In fact if you're doing anything non-trivial I'd recommend not using the OS' provided version of things like emacs, perl, python, ...; best to isolate yourself to the specific version you want controlled by you by compiling your own or using something like docker).
I use this contributed formula which provides some extra options (enabling development / bleeding edge features or different app icons):