What is the ruling on a female nutritionist appearing on television in an interview to discuss useful medical information for people, taking into account the scenarios of her wearing or not wearing a hijab?

There is no harm for a woman to appear on television to present beneficial content, provided she adheres to the Sharia guidelines, such as observing the hijab and not speaking in a soft, alluring manner. If she does not observe the hijab, then it is not permissible for her to appear, because immodest display (tabarruj) is forbidden, whether it is directly in front of people or via the screen.