After the passing of Prince Philip who previously held the title of Duke of Edinburgh, King Charles III did not name his brother Prince Edward, as the Duke of Edinburgh.
According to the reports is seems King Charles is saving the title for Princess Charlotte. Princess Charlotte (7) , The middle child of Prince William and Princess Kate will get the title Duchess of Edinburgh as per the sources. She is the third in line for the British Thorne after her father Prince William and her elder brother Prince George.
The late Queen previously held the Duchess of Edinburgh title, and it would be a fitting way to honor the late Queen and the line of succession according to the sources from the palace.