How is THIS possible at THIS Altitude?

A great number of people have told off Flat Earthers and told them that they don't notice the curvature of the earth because the earth is way too large to feel it. Indeed, the earth is very large, round or flat, it is obtuse. They have said that people have flown about 60,000 feet (Maximum plane altitude) and more above in the sky and have seen a very large curvature come into view. This is very false.

The reason to that is, you see below the image of the horizon at exactly 60,000 feet, the altitude that people say that there is a curvature, and yet it is still as flat as a ruler.

So How is THIS Possible at THIS Altitude and THIS Shape?

You see what I mean? Where is that curvature that people always say they found at plane altitude?