In Windows it’s the same. Though the parameter is -P (uppercase) not -p. That’s why the comment said “it’s hidden behind a startup parameter”.

As best I can tell, there’s no way to make this into a shortcut that you could just click on.

I dont know about Mac, but in Linux you can make a shortcut to call firefox -P. Though what I often do is keep a bookmark to about:profiles and open a new window from there.