20?!

My own view is 4: Antarctica, Australia, America, Afro-eurasia. I'm not sure how you'd get to 3, unless you disqualified Australia.

I've also heard 7: Antarctica, Australia, split North + South America, split Africa + Europe + Asia.

I suppose you could add a few -- I've heard the phrase "subcontinent of India", so that could be an 8th continent. Then maybe Greenland for 9. Beyond that, though? IDK what would even make sense.

BRB, I have to go search for expansive continent definitions.