Never been interested in flat earth theories, but hollow earth sounds a bit more reasonable.
But whatever the physical shape, would proving it's not spherical actually matter very much, other than to confirm the fact that "a few people at the top of the pyramid have been keeping the biggest truths from everyone else for centuries?"
If you found out for a fact it was hollow or a taurus, would you try to go exploring down into it? I wouldn't.
The one theory that makes the most sense to me so far is the Holographic Universe theory. And the way I understand it, this wouldn't mean that nothing is "real" - it's just that there are dimensions beyond what we experience that are more real and more permanent. Some people use the word "illusion" or "simulation" when talking about this theory, but IMO those terms are misleading.
https://www.technewsworld.com/story/72804.html
I can also imagine how this would all tie into the biblical concept of a 2D "book of life" (more likely a scroll than what we would call a book) outside our dimensions, from which all of our 4D existence originates.
But again, other than being intellectually fascinating, I don't know why it would be important for us to prove this. It wouldn't change how we have to live each day or the fact that each of us will exit this temporary Earth sooner or later (all men must die) and face eternity.