I've always had a hard time with flat earthers, not necessarily for their hypothesis, but their absolutely inane arguments.
You can see a water droplet curve on any surface. You can dip a ball in water and see it curve, you can literally try it at home.
But then they move the goal posts, which is infuriating, but at least would move the discourse forward into teaching them about physical phenomena.
As mentioned in other replies, there are both time lapses and live feeds showing movement around a ball earth.
Moon landing can easily be checked by bouncing a laser on the reflectors left by humans there.
The technology to land on the moon might actually be lost (probably not), but it's probably easier than landing on Mars or an asteroid, which has been done. Besides, no space mission relies on "let's do it like we did last time", but careful planning and integration of lessons from every space mission and study.
This is btw also guiding principles for any tricky engineering project.
Also, long bridges, artillery trajectories, and the GPS system all take earth curvature into account. Try talking to an actual engineer.
I will give them that in everyday life you'll almost never notice the curvature of the earth, but then again you'll not notice the limit of the speed of light, electron transmission, bandwidth limits on data transfer (beyond your service agreement ofc), Newton's laws, DNS systems, micronutrient deficits, epigenetics, bacteria/viruses, lions, or microfauna affect on decision making and mood. Hell, a lot of people didn't even notice being neurodiverse or mentally unhealthy until just a few decades ago.
Seems trivially easy to realise that local experience is insufficient to explain things outside it...
Which all lends credence to the idea that there's psychosocial components to conspiracy thinking.