Is there an API to create Notes on OS X ?

I haven't heard of anything like this, so chances are there isn't a framework to do what you're thinking about. However, Apple does accept and consider specific enhancement requests. You can file those using the Bug Reporter tool (bugreport.apple.com); just create an new bug report and choose the "Enhancement" category.

Correct, there isn't an API for this. Please do file a bug report for this if you would like to see it.

Thank you for your replies. I just filed the bug report as Enhancement request.

Additionally, it would be good if a future Notes API had two way syncing of notes in certain folders with other apps that might offer more functionality around notes, i.e. auto reminders, filter by contact name and other tags.

If your application is in Electron or has access to Web APIs you can use the Web Share API to share text to the native Share Cards interface and then to Notes (or any app that can Share Cards)

You can find a demo here: https://codepen.io/ThatGuySam/pen/NWaevbg

Is this the one? https://developer.apple.com/documentation/sirikit/lists_and_notes

I Found a better Notes app. TSNotes it's cross platform and OSS.

https://github.com/glushchenko/fsnotes

I installed on macOS using brew. not sure how to install on my iOS devices… i can buy it but not sure about free installation process yet.