It depends on what you mean by stylus. Technically, a stylus is any pen-like input instrument, so any cheap $4 stylus you find at your local electronics shop would work on the S9, as long as it has a capacitative tip. The problem with most capacitative styli is that the tip is pretty broad, so fine pointing is a little tricky. Wacom does make a capacitative stylus that has a fine point tip:
https://www.androidpolice.com/2018/0...droid-devices/. But if your question is if there's an S Pen-like stylus whose tip can also be used as a capacitative input device, I'm not sure if one is available.