Native form elements have decades of accessibility, autofill, and platform integration baked in. A custom div-and-JavaScript dropdown rarely improves on <select> when measured across screen readers, keyboards, and mobile autofill.
Use autocomplete attributes generously. autocomplete="email", autocomplete="new-password", and autocomplete="one-time-code" all unlock platform features for free.
Pair native elements with progressive enhancement when needed. The baseline experience should work without any JavaScript.