I strongly recommend watching this[1] video about flat-earth belief. It starts with a very impressive direct observation of the curvature, but that's not really the point since flat earth is not a belief based on facts and logic. The video follows the actual history of modern flat earth belief and how it is currently acting as a "gateway drug" into QAnon! (I'm oversimplifying a LOT for brevity)

[1] https://www.youtube.com/watch?v=JTfhYyTuT44

(re: [1] - This is yet another example of algorithmic stupidity: YouTube decided to provide "context" (from wikipedia) about "flat earth" on a video that experimentally disproves the concept. -sigh-)