It's demonstrably false.
Telescopes just make things bigger. If something is hidden beyond the horizon then you won't be able to see it with a telescope.
Here is what one spherical Earth proponent (i.e. reality observer) has said on another forum:
"I zoomed in on this boat. I could see the sail with the naked eye. The bottom of the boat was still covered. Then I stood up so I could see over the horizon and the boat appeared."
You can read more about what his debate with Flat Earthers here:
Help with a debate about curvature and distance calculations
More than likely if you did the experiment yourself, and seen the bottom part of the boat reappear, you either stood up or climbed to a higher part of the boat (i.e. you cheated).
No. You don't understand. You have been tricked by Flat Earthers. Get a 3D program and make a model of a Flat Earth and make a model of a round Earth and test it. If the sun does not go down below the edge than we are not living on a Flat Earth. It is that simple. Perspective of an object getting smaller away in the distance does not make that object drop unless it is being covered by something else. In the case with the Earth, objects drop below the horizon as we get farther away form them because the Earth is spherical. The Earth gets in the way of our seeing the object.