In lore, there are a select few entities that are aware the Destiny universe is a false or lesser reality contained within some larger, "realer" space (our universe). The most well known of these are several (or maybe all?) Ahamkara and Savathun.
The Witness, a being as old as if not older than these entities, with a presumably extensive interaction with the Veil (described as a kind of record of reality itself) doesn't seem to acknowledge this. Why? This seems like a glaring hole in its plan for a Final Shape. Does it just not care what "level" of reality it's on, so long as it has ultimate control over said reality?
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The fourth wall breaks are Easter eggs. There’s nothing canon about it being a false reality. That’s why you don’t see it anywhere else. And if you’re wondering why they would do that, cause they think that sort of cheap crap appeals and makes up for the lack of narrative development.