If the flat Earth was true, hiding it would require the most elaborate conspiracy in the entire world.
The conspiracy would employ tens of millions of people. It's obvious that we would need the involvement of every major government entity - especially (though by no means limited to) their militaries and almost 200 space agencies. Essentially, every professional and amateur astronomer, physicist, geologist, meteorologist, rocket scientist and engineer, architect, pilot and politician in the past five hundred years would have to be in on it. All work they put out, every course, lecture, seminar, and talk, every paper and book, every project, every video, would be built on a lie. It would also mean the Moon landings never happened. Who else would have to be involved? All shipping companies, all airline companies, any transnational company that moves their goods around the world, odometer manufacturers (who would be VERY DEEPLY involved), satellite TV providers. Oh, and let's not forget about cartographers. Furthermore, all of these people need staff, tools, facilities, entire supply chain systems, and they'd be producing meaningless junk, decade after decade.
This conspiracy would also be completely pointless. Life for the vast majority of the human population would not be changed in any way if the Earth were revealed tomorrow to be a giant hockey puck instead of a sphere an oblate spheroid. What would be the point of spending all of this time, effort and money into making people think that the shape of the Earth is different? If you this guy about this you won't get much of a response. this mf might claim that it is "to hide God", even though there are much simpler ways of accomplishing that, like suppressing religion.