I try to learn to make plugins following this site: /

Expecially this one : /

As far as I can see I put all the same code. See my repo:

But in the theme editor and also in the new posts screen I do not see the input box to enter the editorial notes somewhere.

Can someone help me to see if I made a error somewhere in my code or that I misunderstood how this plugin works

I have enabled this plugin and run npm start to compile my code