JSFiddle - React, Tailwind, and code Playground

HTML

<!-- <label for="split">
    Enter the index at which you'd like to split the list.
</label>
<input id="split" type="number" min="1" max="20" value="5" />
<button>Click to split</button>
<hr /> -->
<ul id="list" class="col1 links">
    <li>item1</li>
    <li>item2</li>
    <li>item3</li>
    <li>item4</li>
    <li>item5</li>
    <li>item6</li>
    <li>item7</li>
    <li>item8</li>
    <li>item9</li>
    <li>item10</li>
    <li>item11</li>
    <li>item12</li>
    <li>item13</li>
    <li>item14</li>
    <li>item15</li>
    <li>item16</li>
    <li>item17</li>
    <li>item18</li>
    <li>item19</li>
    <li>item20</li>
</ul>

CSS

a{
    display: none;
}

JavaScript

var ulVal = $('</ul><ul class="links">');
$('ul#list li:nth-child(5n)').after(ulVal)