As Marius van der Knaap mentioned, The Cover Photo Object is empty . All the association and read/Write access you have given is correct. But when you are showing the Course page , the Course_CoverPhoto is empty .
You can make it Editable in many ways
While calling the Edit page, Call a microflow which will have course as parameter then Create a CoverPhoto object and associate with Course entity and then Call your Edit page.
You can Keep a button On the course edit page (Add Cover Photo). Add a Onclick microflow on the button and the microflow will have Course a parameter and Create a CoverPhoto object and associate with Course parameter. Create a pop up which has CoverPhoto as parameter where you can upload the image. In the pop up page you can write your logic in save button.
Hope this Helps !!!!
Most likely the image object is still empty, that's why it appears as non-editable. Make sure to create a CoverPhoto entity and associate it to the Course object, for example on creation of the Course object.
Marius van der Knaap
Give the association Course_CoverPhoto as Read, write not just Read. Also create object for CoverPhoto