It appears you don’t have either version of Classic WOW installed; if you did, you would have a _classic_ and/or _classic_era_ folder alongside the _retail_ folder. You need to run the Battle.net launcher & install whichever version of Classic WOW you want to run.
You should find Battle.net in the same folder that contains the “World of Warcraft” folder. Above the Play button in the launcher there’s a pulldown to select the game version; click on that & select either “World of Warcraft Classic” (for vanilla WOW) or “Wrath of the Lich King Classic”. The Play button should change to Install, click on that to start the installation. When the installation is done (or at least done enough to play) the button will change back to Play and you can launch Classic.
Apparently Blizzard has been aware of this issue for months now that Mac customers are unable to run classic WOW, and they still have NOT fixed the problem.