It’s not easy for an ordinary man to travel into space and directly see the curvature of Earth. But is this really evidence that the Earth is flat?
The ancient scholars didn’t learn about the Earth’s shape by just making things up. They actually were observing the reality around them. And it’s not enough to just look at the horizon and say “the horizon is flat, therefore the Earth is flat”, because a seemingly flat horizon is equally possible and a very big sphere!
One has to dig deep to see the truth for what it is. Looking at the horizon is not enough. Watching YouTube videos with images of flat horizon is not enough. One has to look at all of the evidence and create a model that explains all of the observable phenomena.
And if you have to rely on conspiracy theories to “explain away” facts that don’t fit into your model, it is a sign of weakness of your model.