And also here is footage of a camera that was strapped to balloons that went up so high and you can clearly see a curve.
I don't know if this video could be marked as "shitpost" or not.
I certainly wouldnt, as the efffort these kids put into learning worths respect.
But there are few things I have to say to youngest readers who could take the word "space" seriously.
Helium or hydrogen baloons float in the air.
There is no other way they could lift up.
Air gets thinner with altitude.
99% of the air is below some 30-35 miles or so.
Above that the rest is generally not thick enough to support balloons.
(There's no strictly defined border, thickness decreases gradually.
High altitude balloon record was 53km (32.9 miles).
Generally they go to 37km (23 miles).
Space "officially" begins higher than that, at some 100 km (62 miles).
"There is no definite altitude above the Earth's surface where outer space begins.
However, the Kármán line, at an altitude of 100 km (62 mi) above sea level, is
conventionally used as the start of outer space in space treaties and for aerospace
records keeping."
It is not easy to see curvature of horizon.
They say it is possible from 100 000 ft, but you still have to have wide enough view angle.
Regardless this video, FishEye lense curves straight lines away from center of the view.
If you see that at the center line still looks curved, then it is curved.
It usually gets straightened somewhere further below the center.
In this video most of the time center of view is below horizon.
I only managed to find two brief moments where horizon goes across the center (or does it?).
One is at 4:35, and another at 4:52.
At those two moments horizon looks "free from lense distortions" (and still curved), but sceptics are still free to doubt it.