JSFiddle - React, Tailwind, and code Playground

HTML

<body onLoad="calc()">
  <table id="mytable">
    <tr>
      <th>Header1</th>
      <th>Header2</th>
      <th>Header3</th>
      <th>Header4</th>
      <th>Header5</th>
      <th>Header6</th>
      <th>Header7</th>
      <th>Header8</th>
      <th>Header9</th>
      <th>Header10</th>
      <th>Sum</th>
    </tr>
    <tr>
      <td>2022</td>
      <td>Januar</td>
      <td></td>
      <td>22.40</td>
      <td>11.10</td>
      <td></td>
      <td></td>
      <td></td>
      <td></td>
      <td></td>
      <td></td>
    </tr>
    <tr>
      <td>2022</td>
      <td>Februar</td>
      <td></td>
      <td>2.40</td>
      <td>11.10</td>
      <td></td>
      <td>17.50</td>
      <td></td>
      <td></td>
      <td></td>
      <td></td>
    </tr>
    <tr>
      <td>2022</td>
      <td>März</td>
      <td></td>
      <td></td>
      <td></td>
      <td></td>
      <td></td>
      <td></td>
      <td></td>
      <td></td>
      <td></td>
    </tr>
  </table>
</body>

JavaScript

function calc(){
	document.querySelectorAll('#mytable tr:not(:first-child)').forEach(function(row){
		var sum = 0;
		row.querySelectorAll('td:nth-child(1n+4):not(:empty)').forEach(function(col){
			sum += parseFloat(col.innerText);
		});
		row.querySelector('td:last-child').innerText = sum.toFixed(2);
	});
}