
Who looks DOWN from a mountaintop to see the horizon?
Everyone. But your diagram is ridiculously out-of-scale. The earth’s radius is about 4000 miles. Even a person standing on Mt Everest is not at 4000 miles altitude above mean sea level.
Your diagram is ridiculously not to scale ... it suggests an Earth diameter of 1516 meters. QUIT LYING.
I will not waste time on your sentence, but
Eight Inches Per Mile Squared - FlatEarth.ws
https://www.perplexity.ai/search/what-is-the-raio-of-105-office-98lmZhzARESy7SsdfbTnpg#18,
https://www.sciencefocus.com/space/how-to-argue-with-a-moon-landing-denier
https://jacquesgaines.com/2020/11/28/photographic-proof-we-went-to-the-moon/
Discussion.....Earth Shadow "Zone of Venus"
Better Diagram:

Who looks DOWN from a mountaintop to see the horizon?
—
I did, Kitt Peak, sunset. The shadow of the mountain converged at infinity above the horizon. It was a spiritual experience.
I hope you are not presenting the flat earth argument that the curvature of the Earth is a parabola.
The equation for a parabola is incorrect for a sphere, y ≠ 8⋅x².
Distance to Horizon calculator:
https://www.omnicalculator.com/physics/distance-to-horizon
I once calculated the formula for this and then tested it from the Handcock Tower in Chicago. Sure enough Island’s in Lake Michigan which you could not see from the shore you could see from the top of the tower.