What are the requirements for a province to show up as a viable cede option when negotiating peace?
Solution 1:
I believe Marrakech is the capital province. It's hard to see in your photo, but I think you will see a crown on top of a pole coming out of the map in that province -- that indicates it is a national capitol.
You would receive that province as part of a full annexation, but you can't just take the capital as if it were any other province.