ESM is a defined default you find back in ECMA specifications. That is why everybody should migratie. Node.je is also moving ESM to the default. If some systems dont do it, dont use it anymore. That it went i dont use jest anymore, and Node.js has also now a good test runner. (Useful for packages and backend systems, i think for frontend systems with eg React there are better test suits to help with special frontend stuff like the DOM)