I told you exactly what the gif is,
It's a sphere scaled to the size of the earth.
The camera originates at the top center on the surface of the sphere, and then ascends at a 90 degree angle until the horizon is no longer visible.
But you're more concerned with where the gif came from.
How bout this,
- go in a 3D program, create a sphere.
- Scale it to the size of the supposed globe earth (24,901 miles = 131,477,280 feet).
- Add a camera and set it at the top of the sphere.
- Animate the camera so that is ascends along the Y axis until the sphere is no longer visible.
- Render it.
- Convert it to a gif.
- Upload the results and show me what you got.
That doesn't make any sense. In one set of key strokes you say round Earth doesn't exist. Yet in another set of keystrokes you say, "Scale it to the size of the supposed globe earth (24,901 miles = 131,477,280 feet)." Why does any part of your explanation of flat Earth include specs of global Earth? Especially the circumferential distance which leaves you with half a globe if looking from the top of a sphere. If I take a ball and draw a circle around the center of that ball. Then hold it from the bottom and face it to you. You will not see the line or the bottom of the ball. Therefor taking the face value of that ball would leave out the total mass of the other side of the ball. There are over 196,000,000 square miles of global Earth, that will not fit on flat Earth you describe.