That depends.
You could be asking whether the man who happens to be the current pope, Francis, is Catholic. You would then be asking about the occupant of an office at the apex of the Catholic organizational hierarchy. Or you could be asking about the office itself: Is the office of the papacy occupiable only by a Catholic?
The answer to the second question is easy: of course.
The answer to the first question is not so easy. Is Francis a loyal Catholic who upholds authentic Catholic teaching? Many in the know are skeptical. See here and here. I agree with them. Those links are to First Things articles. The Remnant takes a harsher line.
So there is a clear sense in which the pope is not Catholic.
I suspect that his real 'religion' is leftism.