It can be readily observed through simple optical instruments, namely telescopes, which you could purchase yourself, and in an area where the sky is amenable to observation (mountainous areas with minimal light pollution are ideal), you could observe, among other things, celestial objects not visible to the naked eye and the motion of the planets in space, for example, you could with relative ease track the motion of Uranus, which cannot be seen without a telescope, but can be seen with them. And using larger telescopes such as those installed in a university you could perhaps see the rings of Saturn (although in 2025 they will on two occasions be invisible due to their orientation towards earth, and 2025 would not be a good year for viewing them).
Likewise I have repeatedly urged you and
@JacksBratt to organize fellow flat Earthers to charter a flight from Buenos Aires to Melbourne, which will take you almost directly over the South Pole, or you could actually visit Antarctica and see the South Pole from the nearby McMurdough Research Station. Or you could take one of the intercontinental flights in the Southern Hemisphere which do actually exist and compare the travel time with what was expected. But the flight time from a trans-polar flight from Buenos Aires to Melbourne would literally be impossible in the flat earth model, so if a giant ice wall exists in Antarctica as is claimed that would be the surest way of finding out.
Until then as I see it this is simply a claim without evidence to support it, whereas the evidence in favor of the geodesic Earth is frankly overwhelming and consists of far more than fake photo manipulation and CGI. For example, the specific travel times between different points of the voyages of Prince Henry the Navigator, Ferdinand Magellan, and other explorers of the Southern Hemisphere, and old naval logbooks which preserve this, as well as records of flights operating on routes you claim do not exist, et cetera.
Now I wouldn’t actively debate this except for the fact that it is being claimed as a matter of Christian doctrine, which is not only untrue but poses an active impediment to evangelism. The controversial point of Christian doctrine is and always has been Christ Crucified, so when people raise other doctrinal issues to an extreme level of prominence, it detracts from the central message. For example, I am extremely sympathetic to young Earth creationism and there is an approach, which I would call the pre-optimized cosmological approach, wherein God could be said to have created the world in seven days with the parameters it would have as if the universe was 13 billion years old, and this creation through the conversion of a simulated reality to an actual reality would make sense if the creation of humanity was the primary objective of the creation of this universe; that said, when people stress an anti-intellectual approach to Young Earth Creationism which does not bother to explain the evidence contradicting it, and build theme parks about it, and debate with Bill Nye (who is an unpleasant man in my opinion due to his atheism and political activism, and an entertainer, not a scientist, who misrepresented among other things how one of the illusions in the Haunted Mansion worked on his program on the Disney Channel in order to facilitate a segue into holograms, and is not worth being debated with) not worth debating with) and make it the main point in textbooks for Christian education, this all collectively detracts from the central Gospel message of the Passion and Resurrection of our Lord and our hope for resurrection that this entails.
Frankly, in the grand scheme of things, the shape of the Earth is almost entirely irrelevant next to the Incarnation of the Only Begotten Son and Word of God in the person of our Lord, God and Savior Jesus Christ. But by making it an issue, this creates a needless impediment to people hearing the Gospel, just as those who over-emphasize Young Earth Creation or insist upon the sole inspiration of the KJV (discussion of which finally had to be banned on CF.com a couple of years ago) create controversies which are distractions from the essential task of evangelism, which is, as St. Paul said, preaching Christ crucified.