You made a spelling mistake change your code to.

window.addEventListener('DOMContentLoaded', () => listdata());

Instead of

window.addEventListener('DOMContentLoarded', () => listdata());

or you could use

window.onload = () => {
    listdata()
}

How about this?

const container = document.querySelector('.datalink')
let listdata = async() => {

    let url = '  http://localhost:3000/indusboards';
    const urlfetch = await fetch(url);
    const urlfound = await urlfetch.json();
    let template = '';
    datafound.array.forEach(element => {

        template += `
             <div class ="element">
             <p><small>${element.serialno}</small></p>
             <p><small>${element.boardtest}</small></p>
             <p><small>${element.testresul}</small></p>
             <p><small>${element.serialno}</small></p>
             <p><small>${element.testdate}</small></p>
             <p><small>${element.testtime}</small></p>
             <p><small>${element.boardlocation}</small></p>
             <a href = "/json_projet/details.html">.... more</a>
             </div>
         
         `
    })

    container.innerHTML = template;
}


window.addEventListener('DOMContentLoaded', () => listdata());