firstUpdated()

<uui-box headline="Sortable List" style="margin:20px;">
            <ul class="list-group m-3" id="items">
                <li class="list-group-item">item 1</li>
                <li class="list-group-item">item 2</li>
                <li class="list-group-item">item 3</li>
            </ul>
            </uui-box>

firstUpdated() {
        const items = this.shadowRoot.querySelector('#items') as HTMLElement; // Cast items to HTMLElement
        if (items) {
            new Sortable(items, {
                animation: 150,
                //handle: '.list-group-item', // Not really needed in this case
            });
        }
    }