In SharePoint Online at times you might encounter that you cannot add or import term sets even after being a site collection administrator. Especially in the small business plans where there is no SharePoint Admin Settings and you might be wondering how to get started with adding terms to the term store. In such cases when you navigate to Site Settings—>Term Store Management you might see something as below which does not allow you to add or import anything. Worry not the solution is simple, navigate to Site Collection Features and activate the SharePoint Server Publishing Infrastructure Feature And head back to term store management, you should now see a new group and now you can start adding the terms.
You can add a custom action to the feature by providing the ImageUrl property
Also, for custom actions you can also do the same