Ok so the entire thing of the realm of ideas is that it's not the Platonic stuff that may you think of (don't blame yourself, is just powerscaling rot).
The whole essay is about people becoming immortalized through their stories, due to these stories being forever remembered across generations, thus allowing one's identity to become an idea that will forever exist across human mind, allowing one to have their identity tuned in an idea that will never die, and that will forever influence others' consciousness and thinking. Because of this, Bill describes it as a cycle of fiction and reality creating each other.
This isn't how Plato's actual realm of forms works, which instead are concepts that exist in a realm that is both aspatial and atemporal, with the concepts and objects of the physical world being only shadows of the forms, with anything of the latter being unable to neither reach nor change the forms.
Context is key, you don't just throw Plato in just because the name is coincidentally the same, when the Mindscape works as anything but the actual Platonic Forms.