how to use addEventListener with the new customizable

I am referring to customizable <select> described at https://developer.chrome.com/blog/rfc-customizable-select.

All works as described; but I hit a wall trying:

document.querySelector('select').addEventListener('change',dropdownHandler);
// or
document.querySelector('selectedoption').addEventListener('change',dropdownHandler);

as no event gets fired […or I’m just a noob].