No, the act of someone with the power to travel to fictional universes physically entering a fictional universe would not make that universe "real" in the sense that it becomes an actual existing universe within our reality. The fictional universe would still remain a product of imagination and storytelling, separate from our physical reality.
When we talk about fictional universes, we are referring to imaginative constructs created by authors, filmmakers, game developers, and other creators. These universes exist within the realm of fiction and are typically governed by their own rules, laws of physics, and narrative structures.
While the person traveling to the fictional universe may experience it firsthand and interact with its characters and elements, it would still be within the confines of their own subjective experience or imagination. The fictional universe itself would not suddenly manifest as a tangible reality accessible to others outside of that individual's perception.
It's important to distinguish between the concept of visiting a fictional universe as a narrative device or imaginative exercise and the notion of transforming a fictional universe into an actual, independent reality. Fictional universes remain products of human creativity and remain confined to the realm of fiction, even if someone were to explore them in their mind or imagination.