Honestly, I was just on a Carnival cruise as a solo and they had a scheduled solo meet & greet every day - but it was NOT hosted and frankly just a waste of time. I did not see anyone there identifying themselves as a single cruiser.
I suggest Norwegian Epic (first) or Breakaway or Getaway) as being better for solo cruisers - they have true solo cruiser programs on every cruise.
I am the editor, but I also speculate, ask questions and play devil's advocate. I reserve the right to change my mind.