I have a website where authors write articles, but can not publish the article. An editor first has to check and approve the text. We have a plugin that notifies the editors when a new article is added or changed. Sometimes a text is added, but the author still needs to add some extra information or needs approval from the photographer to use an image.
Now the author needs tot contact the editors separately via e-mail or messenger to ask them not to publish the article yet.
Would there be an option to add (hidden) comments / remarks to an article for internal use?

Are you referring to: github.com/getk2/k2-example-plugin ?
What I would like is that the author can add notes via the frontend. The notes should only be visible to the author and the editor. That would be possible with the plugin?