Heads are round but a beard can have corners. If you think this passage means that the Earth is flat and square, you also have to make the case that human heads are square. Good luck with that.
Extremity, extreme part, corner: כַּנְפ֥וֹת – kanaph
To cease, fail, have and end: אַפְסֵי – ephes
If my feet are at the end of my legs, then the coast is at the end of the land. The ends of the earth is simply where the land stops: it ceases, fails, has and end. The beach.
The Ends of the Earth
If the Earth has ends does that mean it has to be flat? No, because "end" is a translation of a word which means "extremity or furthest reaches of" in which case we're talking about the beach.
The Sons of Noah
The time between Noah's flood and Peleg's tectonics was when the dispersal from Babel took place. From Babel small family groups spread out, figuratively speaking, to the ends of the Earth.
Brachiopods
Brachiopods aren't an evolutionary dead-end which got wiped out in a mass extinction. Well, there was a mass extinction, but it didn't wipe out the Brachiopods. Many were buried in Noah's flood but many alive today.