react is creating iframe

Question

I'm new to react and I have a really basic code

import React from "react";
import ReactDOM from "react-dom";

ReactDOM.render(
    <h1>hello</h1>, 
    document.getElementById("root")
);

When this page renders there's an iframe inside my body.
Here's what it looks like

the script inside the script tag was really big, it took me around 5 seconds of rapid scrolling to reach the end. In the tutorial I'm following, the tutor did not get this iframe. Why am i getting it? And how do i remove it? thank for your help!