Question

What separates the continents of North America and South America​

Answer 1

If you mean physically? The definition of a continent is a large, continuous, discrete mass of land, ideally separated by an expanse of water. so the Caribbean Sea, or the Panama Canal

Answer 2

The border between North America and South America is at some point on theIsthmus of Panama. The most common demarcation in atlases and other sources follows the Darién Mountains watershed divide along the Colombia-Panama border where the isthmus meets the South American continent.