RE: Is this a 3D world or just a data structure?
"3D" presumably assumes spatial dimensions. Whereas "data structure" implies mental dimensions, or a mindfield. Advaita vedanta surely rests in a mental field, not in physical space which would require explanation for its existence.
Active minds assume mental dimensions to act or move in. Such dimensions may be conceived and/or perceived as spatial, but they are assumed or produced by mind.
Advaita, or nonduality, is Reality, or realisation that there is no space out there separate from any observer in here. All is a play, or creation, of mind. Other words may be used instead of "mind" e.g. heart, soul, spirit,... This whole exercise of explanation in words, or "data structure", is dualistic. All such finite data is nothing but symbols shuffled, juggled or played around with.
Reality needs none of it. But boundless nothingness, or emptiness, allows finite minds to play around or suffer in their own little worlds, or mental structures.
Reality dissolves, or solves, all data, dimensions, and structures.
Nothing but dreams, mirages, illusions and delusions. Such are the stuff of creation. Humans are agents making their own worlds and imagining they are separate subjects existing in an objective world. That is duality. Duality is the Devil!