If "exist" means objectively real, independent of any mind: No. Magical thinking, by definition, relies on belief in supernatural forces or causality that don't operate within our scientifically understood universe. A fictional world created by magical thinking would only exist as a construct within the mind(s) of the believer(s). It wouldn't have an independent physical reality.
If "exist" means existing as a shared imaginative construct: Yes. This is how most fictional worlds operate. Authors create them using their imaginations, and readers engage with them through shared understanding of the author's created rules and systems. While the stories are not objectively real, they exist as potent and meaningful experiences within the minds of the author and the audience. The creation and shared understanding of these worlds can involve elements reminiscent of magical thinking—the author imbues the world with impossible powers or events, and the reader willingly suspends disbelief to accept them.
If "exist" means having some effect in the real world: Yes, in a limited sense. Fictional worlds can inspire real-world actions, influence culture, and shape beliefs. The power of a fictional world lies in its ability to impact the human experience, even if it isn't objectively real. This influence is not, however, due to inherent magical properties of the world itself, but rather the psychological and social effects of engaging with powerful narratives.
Therefore, while fictional worlds *cannot* exist in an objectively real sense through magical thinking, they can certainly exist as powerful imaginative constructs and have real-world consequences, even if the process of their creation and engagement shares aspects of magical thinking (like accepting fantastical elements as real *within the context* of the story). The key lies in the distinction between the internal logic of a fictional world and the external reality in which it is conceived and experienced.