Oh yes Dolly Parton! She can’t be horrible, she just can’t!
I have seen first hand how someone in the public eye can build a nice (or funny/ditsy/witty/kind etc) persona, it’s part of what they do. The person I know IRL - a pop singer - isn’t horrible or mean, she’s just self-interested and hard as nails. If she wasn’t, she’d be unlikely to have done so well. But the person she is is not what you see in interviews etc. A lot of “lovely” celebs probably are not.
However some must actually be nice people by the law of averages, so I still hold out hope for my favourites.