Hi Kris,
Unfortunately MapNote can't be created using the API right now. But it will happen soon.
Good news - there is a workaround though. Can you please try this?
*Using the Pro UI:
* add the Map Notes you want to the map. (I can help you with this if you need. Here is the help link: Map notes—ArcGIS Pro | Documentation )
* Save the Map notes as a layer file (using the sharing tab). These 3 steps are a one time process to store the MapNotes as a layer file.
Then using the API:
* Add the layer file to the active map.
* You can now start graphical features to this map notes layer using MapPoints, Coord2D, etc. Instead of using Overlays, you would just be adding features to the map notes layer.
* These can be exported.
Please let me know if you run into issues.
Thanks
Uma