This corny meme implies that philosophy majors become flat-earthers, etc.

No, most philosophy majors still believe in gravity. While flat-earthers cease to believe in gravity once they realize that a flat earth is incompatible with gravity. They replace it with this notion that the earth disc (and the rest of the system) is accelerating upwards through the void at 9.8 m/s^2.

Though I’ve come across some interdisciplinary studies types who would probably argue that gravity is a social construct because we describe it with language.