A postdoctoral fellow refers to a person who engages in scientific research in an institution of higher learning or research after obtaining a doctorate, usually in a postdoctoral mobile station or a postdoctoral research center. It should be noted that postdoctoral fellows are not degrees, but work experience.
Therefore, the extension of visiting scholars is wider than that of postdoctoral fellows. The reason why the National Scholarship Foundation named the project "National Public Visiting Scholar Project (including postdoctoral research)" is also because it believes that postdoctoral research belongs to the category of visiting scholars. Based on the above analysis, if you don't have a doctorate, then obviously you can only apply for a visiting scholar, not a postdoctoral fellow.