Missing App extensibility and custom field?

I just got the new job and the SAP Marketing Cloud version:2202, however someone who implement this platform have quit and doesn't leave any document to me.

I have been request to add custom field to Contact's additional data, I search all around the forum, it seem I have to do it via App extensibility -> custom field, but I wonder why I have this section, see the screen shot below:

If I mouse over right-top corner profile icon, even-thought I found the Extension, but it does not allow to search and import anything, so what is the reason and any recommend