how to make javascript scrollIntoView smooth?

This might help.

From MDN documentation of scrollIntoView
You can pass in option instead of boolean.

scrollIntoViewOptions Optional
A Boolean or an object with the following options:
{
  behavior: "auto"  | "instant" | "smooth",
  block:    "start" | "center" | "end" | "nearest",
  inline:    "start" | "center" | "end" | "nearest",
}

So you can simply pass parameter like this.

scrollToQuestionNode(id) {
  const element = document.getElementById(id);
  element.scrollIntoView({ block: 'end',  behavior: 'smooth' });
}

Reference: https://developer.mozilla.org/en/docs/Web/API/Element/scrollIntoView