i've actually taken to debating a few flat earthers on youtube
seems like they always forget things like:
How perspective works > anything above you that moves away parallel to the ground converges with the horizon, you always have to look 'up' at it, ever so slightly, until it becomes so tiny you can't see it. there is no way that something that moves away parallel to the ground, above you will ever sink below a horizon. it's a physical impossibility that's that's not what happens with the sun.
Planets - planetary movement doesn't make sense on a flat earth. if there is a solid starfield with little lights overhead, why do the planets move independently from the stars? why is it that when we look at planetary bodies with telescopes they appear to be round?
moon - they cannot explain why the moon pases through earth's shadow creating lunar eclipses
maps - they cannot figure out a map that works. I saw a video by one guy who genuinely tried. he started with some major cities, plotted them out as points on a blank sheet and modified a map over it. he could not make it work with the magnetic north and south still making sense. it was the most clever attempt I had seen and even that person was like: yeah this is a bunch of horseshit....