DOM is not being uploaded for my Etch-A-Sketch board – Blancer.com Tutorials and projects

Receiving the following error when trying to run the below code: Null value on line 9 due to appendChild. Is my code not reading the etch id?

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <script src ="script.js" defer></script>
    <link rel="stylesheet" href="style.css">
    <title>Document</title>
</head>
<body>

    <div id="etch"></div>


    
</body>
</html>

let num = 16;

let etch = document.getElementById("etch");

function board () {
    for(let i = 0; i < num; i++) {
        let row = document.createElement("div");
        row.classList.add("row");
        etch.appendChild(row);

    for(let j = 0; j < num; j++) {
        let column = document.createElement("div");
        column.classList.add("column");
        row.appendChild(column);
      }

    }
 }

 board();

*{
box-sizing: border-box;
margin: 0;
padding: 0;
}

#etch{
    margin: 27px;
    display: flex;
    flex-direction: column;
    width: 500px;
    height: 500px;
    border: black 2px solid;
}

.column{
    display: flex;
    flex-grow: 1;
    background-color: silver;
}

.row{
    flex-grow: 1;
    border: white 1px solid;
}

I am able to get my code to work in MDN playground earlier without adding external js or css files. Not sure what’s going on here. I would appreciate any help. Beginner here.