The way ships on water can be "brought back" with a high zoom camera, and mountains/buildings in the distance staying STRAIGHT UP and VISIBLE LONGER THAN THEY SHOULD BE are two of the biggest arguments for Flat Earth that I've found so far.
If a skyscraper were super tall and very far away, to your left OR right, and part of the "missing bottom" was below the horizon, you wouldn't just have half of the skyscraper sticking up straight perpendicular to the ground, as it was when it was 20 feet in front of you! If the explanation was "the earth's curvature made the bottom half disappear from view" then the other half would be leaning one direction or the other -- certainly "backwards" away from you, but also to the left/right unless the skyscraper was RIGHT IN FRONT of you.
Get out a globe and test it. Think about it.
I never thought of that, until I watched one of those videos. VERY convincing. In fact, despite many other unresolved questions I have about Flat Earth, I can't imagine a globe-friendly explanation for this obvious, common-sense, down-to-earth evidence that anyone can test/repeat.
Remember, the number of scientists trying to figure out how Flat Earth works is almost non-existent. Just a few laymen (amateurs), really. So having an unresolved mystery, an unanswered question or 100 should NOT be a dealbreaker, logically speaking. It is logical to have many unanswered questions, given the resources, time, and personnel being thrown at this subject at present.
However, if there are 1 or 2 valid proofs for Flat Earth, out of all the chaff, controlled opposition, intentional disinformation, etc. then the whole Globe Earth house of cards comes crashing down: it becomes a lie. Prove JUST ONE LIE, and the whole thing is a ball of lies that unravels. NASA wouldn't just lie about one thing. Once they are proven liars, they are not to be trusted, and it's LOGICAL TO CONCLUDE they have a whole web of lies to defend their whole "system" or "Big Lie". It is not necessary to come up with courtroom-worthy evidence or proof to debunk EACH of their lies.
All we need to do is come up with compelling, concrete evidence that most laymen can understand (with common sense) that proves NASA is lying to us.