“Harry Potter is a wizard.”
That is, “Harry Potter” is the name of a fictional character in a series of popular novels, and that character is a member of the imaginary class of people known as “wizards”, who (in the context of these fictional narratives) are able to use “magical spells” (reciting “Dog Latin” whilst waving around “magic wands” that have been constructed in certain specified ways) to affect the world. Like, they can straight up kill a motherfucker, even.
(Of course it would certainly be possible to write a series of books about a character who maybe has magical powers, but maybe he doesn’t really have magical powers, there are actually mundane explanations. In fact, that sort of thing has been done many, many times over. But that’s not the Harry Potter novels. In the Harry Potter novels Harry Potter is, no doubt about it, a wizard.)
Anyway, saying that the fictional character, Harry Potter, in the context of the eponymous books–in that fictional “universe”–has the power to do this and that is perfectly sensible. (“Oh, I love the Harry Potter books. Of course I don’t believe he can fly around on a broomstick or do magic, or any of that; I just enjoy them as the story of a young boy with profoundly psychotic delusions who has created a whole hallucinatory life for himself in response to severe and prolonged childhood abuse” would be…well, it’s a free country, but it would be a weird reading of those books, that’s for sure.)
Saying you believe that Harry Potter is a real person, and really has magical powers, is consistent. (Albeit totally unsupported by any actual evidence, and frankly daft.)
Saying that Harry Potter is a fictional character, and that of course “wizards” don’t exist in the real world, but that you nonetheless admire Harry Potter’s (fictional) personality traits–pluckiness and bravery and loyalty to his friends and so on–or that you like the moral and emotional message of those books (e.g., “love is stronger than hate”) is perfectly defensible as well.
Saying that Harry Potter is a fictional character, and does not really exist, but also that Harry Potter is “really” a wizard, doesn’t make any damned sense.
And saying I don’t believe Jesus really existed or exists, but I do believe he is “the Christ”–that is, the Son of God is like that last example. Being a “Christian” is saying that Jesus of Nazareth (a person who putatively actually lived at one point) is “the Christ”. “Jesus of Nazareth” could be a “moral exemplar” in the same way “Harry Potter” can be a “moral exemplar”, regardless of whether either of them ever actually lived. But it’s weird and misleading to claim to be a “Christian” (“one who believes Jesus of Nazareth is ‘the Christ’, that is, ‘the Son of God’, however ‘Son of God’ is defined”), while also believing that Jesus of Nazareth is a fictional character.