test

HTML

<body onload="myFunction()" oninput="myFunction()" style="zoom: 225%">
    
  <select name="" id="element0">
    <option value="test1">test1</option>
    <option value="test2">test2</option>
  </select>

  <div id="element1">
    <label for="your-name">Name: </label>
    <input type="text" name="your-name" id="" />
  </div>
</body>

JavaScript

function myFunction() {
        if (document.getElementById("element0").value = "test2" ) {
            document.getElementById("element1").disabled=true;
        } else {
            document.getElementById("element1").disabled=!0;
        }
    }