See, I love stories like this of taking concepts and just playing around with them. I would start with both the base premise of the Flat Earth theory as well as look up things like Terry Prachett's Discworld. I also like looking up ancient civilizations and their believes and tweaking them to serve a story.
the gravitational situation on a disk-shaped world might also offer a few interesting starting points for stories. And if I recall my physics lessons correctly, towards the rim people would walk not straight up but at an angle.
Plus all the air and water would want to pile toward the centre. Spinning the disc once per day would mitigate this but not to the extent of flattening the atmosphere and ocean into what we observe.
In any case, a flat disk the size of the Earth couldn't exist. Any rocky body approximately 1000 km or more in diameter will be pulled into a spherical shape by its own gravity. Link: https://astronomy.com/magazine/ask-astro/2017/08/the-diameter-of-spherical-bodies Of course, the Flat Earthers get around this little paradox by claiming there's no such thing as gravity!
Yeah but they can't ever explain then why things don't float off the ground. Or why they can't float off into space if gravity doesn't exist.
Bayes theorem tells us the odds that the flat earth hypothesis is correct are essentially zero. The odds on the flat earth hypothesis being correct over spherical earth = (prior probability of flat earth hypothesis being true x consequent probability of the available evidence supporting a flat earth) / (prior probability of spherical earth hypothesis being true x consequent probability of the available evidence supporting a spherical earth) I could easily come up with thousands of pieces of evidence that support the spherical earth hypothesis - photographs being the most obvious - but none that support the flat earth hypothesis. All proposed evidence for the latter is false, being based on logical fallacies, magical thinking, and subjective bias. So even if the prior probabilities are 0.5 and 0.5 - no knowledge either way - the posterior odds that the flat earth hypothesis is true given the evidence are 0.5 x 0 / 0.5 x 1 or zero. It's not worth one second of anyone's time considering such nonsense.
All you can do is change one mind at a time. And that works best at the personal level, not via the Internet.
It does seem like a tsunami of bilge - flat earth, hollow earth, the elite being space lizards, moon landings being hoaxes, vaccines being a government plot, 5G being behind Covid-19... Are the same nutters/bots/antagonists behind all of these or has the world truly gone mad?
I think the nutters have always been there but, never have they had as much ability to be heard than now... Welcome to the (very) bad side of the intertubes...