Hi Syabab,

They depend on these factors.
- is the related app published or not
- is the user able to access the related app(access control setting in the app)
- is the feature disabled on EasySocial(eg: videos feature disabled on EasySocial)
- does the user have permission to create related item(eg: cannot create videos)

How can I add 'Notes' app button there?

You cannot do so through settings because the notes app does not have a button on the story panel.