Yes.
Advanced Search can only find Tasks and Conversations; it doesn’t return Projects. So the best you can do for this directly in Asana is run the Advanced Search and Sort by Project, then manually modify project-level notifications one by one. Not what you wanted, I know…
There is a fast workaround that I recommend that may save you some headaches: see Email notifications for ONLY tasks you have been tagged in - #2 by forlaurn and scroll down to my Mar 12 comment.