Hi @thiagoleitebr;
Let me clear that for you. Department gets its featured image from the newest portfolio post under that department. Example;
You have a department named “C” and under it you have added to portfolio posts.
Then lets say that you add a portfolio post which named “A” and then after that you have added another portfolio post named “B”. They are both under the department “C” In this case in your portfolio page department C’s featured image will be same with portfolio A’s featured image (The latest post added under this department) .
Thanks