The sun is round, the moon is round, the stars are round

Biconvex vs Globe should be the original argument. Disc vs Ball.

Do flat earthers think of sharp edged biconvex earth? Like that would have had to be the case if you could sail off it.

Do they think that it's like a Minecraft world where they could see the dirt under the grass at the edge?

Humans had to explore the globe W-E or E-W. No practical way early to cross a frozen tundra and then sail going N-S or S-N.

We would have found out a lot quicker in human history if the polar caps didn't exist.

"Go around" round. It is almost like it is intuitive that the earth is round.

What's happening at the edge is what is the argument. Everyone knows where they are standing is flat. (Which I think is your point)

You'd have to come up with a plausible explanation of what could happen. Like "You'd sail off into a void"

Yet a globe has no edges and doesn't need a plausible explanation about a weird edge of the earth.

It should have aways rested that you had to prove the earth wasn't a ball.