Now that linked mentions are shown as backlinks, there should be a special search to see orphans (notes with no incoming or outgoing links). I posted some ideas for improved search features last year. Unfortunately, it’s something further down the road.
In the meantime, this will work.
No outgoing links:
-[[
No incoming links (assuming all links start with a letter or number):
-[[a -[[b -[[c -[[d -[[e -[[f -[[g -[[h -[[i -[[j -[[k -[[l -[[m -[[n -[[o -[[p -[[q -[[r -[[s -[[t -[[u -[[v -[[w -[[x -[[y -[[z -[[1 -[[2 -[[3 -[[4 -[[5 -[[6 -[[7 -[[8 -[[9 -[[0
Save as search action.