> the last 2 LTS releases of Node

(Author here.)

Node 14 supports ESM, but Node 12 only supports ESM behind the --experimental-modules flag, and its error handling for incorrectly importing CJS is not good.

In 2020, I think it's a bit early to go ESM only, especially since it's straightforward for CJS libraries to support both CJS and ESM clients. (I document how to do this in the article.)