function Foo() {
  // - If possible, prefer as specific as possible. For example, HTMLDivElement
  //   is better than HTMLElement and way better than Element.
  // - Technical-wise, this returns RefObject<HTMLDivElement>
  const divRef = useRef<HTMLDivElement>(null);

  useEffect(() => {
    // Note that ref.current may be null. This is expected, because you may
    // conditionally render the ref-ed element, or you may forget to assign it
    if (!divRef.current) throw Error("divRef is not assigned");

    // Now divRef.current is sure to be HTMLDivElement
    doSomethingWith(divRef.current);
  });

  // Give the ref to an element so React can manage it for you
  return <div ref={divRef}>etc</div>;
}