Toad Mac Edition does not support simultaneous Toads running at a time. For now, users can see the multiple copies option right now, and this will be hidden for Toad on Mac in future versions.
Mac apps just are not designed to run this way, but, if you choose to do so, you can find out how to do it using the Mac terminal with a google search. Here is one link that can help:
https://www.makeuseof.com/tag/run-multiple-copies-app-mac/