The truth is, I can make sense of your first two sentence up to "dropbox", but from that moment you loose me.

  • what is it you call a sync wizzard
  • and if you erased your harddrive, how is Joplin supposed to find the folder "already on DB", and what does "on DB" mean anyway ?

Do me a favor and look into menu -> options -> sync -> "show advanced....
it may solve your problem on Mac.