The phenomenon you described, where land appears to emerge from a distance when viewed through a telescope, is not evidence against the notion of a curved Earth. In fact, it is a result of the Earth's curvature and the way light behaves.
When you observe distant objects, such as land or ships, there is a limit to how far you can see due to the Earth's curvature. As you increase your distance from an object, it gradually disappears below the horizon due to the curvature of the Earth. This is why ships seem to "sink" as they sail away from shore.
However, under certain atmospheric conditions, such as temperature inversions or atmospheric refraction, light can be bent or refracted in such a way that it follows a curved path. This bending of light can cause distant objects to become visible again, even though they are technically still beyond the curvature of the Earth.
In the case of using a telescope, the magnification power of the telescope can bring objects back into view that are beyond the horizon due to the curvature of the Earth. The telescope can gather and focus more light, allowing you to see objects that would otherwise be too small or too far away to be seen with the naked eye.
So, while it may appear that land is "emerging" or coming back into view through a telescope, it is actually the result of the curvature of the Earth and the bending of light rather than evidence against it. The overall body of scientific evidence, including observations from space, satellite imagery, and numerous other measurements, strongly supports the understanding that the Earth is indeed curved.