At What Height is the Earth's Curvature Visible?

This video poses a very simple question

"At What Height is the Earth's Curvature Visible?"

For such a very simple question we don't get a very simple answer.

Instead we get multiple different answers to this question and nobody ever admits they may have been wrong about what they saw.

As you can see in the comments people just can't decide on a for sure height to where one can definitely see the curvature of the earth.