Не может блокировать поля, когда отмечена кнопка проверки

Сюда...

const 
  inputsForm = document.querySelectorAll('input.block')
, checker    = document.querySelector('#scale1')
  ;

blockFileds()
checker.onclick = blockFileds


function blockFileds()
  {
  inputsForm.forEach( singleField =>
    {
    singleField.disabled = !checker.checked
    })
  }

.block, label {
  display : block;
  margin  : .3em 0;
  }

<div class = "container">

  <input type = "number" class = "block">
  <input type = "text"   class = "block">
  <input type = "email"  class = "block">
  <label>
    <input type = "checkbox" id = "scale1" name = "scales">
    Scales
   </label>

</div>

вы можете попробовать это:

const inputsForm = document.getElementsByClassName("block");
const checker = document.getElementById("scale1");

function blockFileds() {
  for (let singleField of inputsForm) {
    if (!checker.checked) {
      singleField.disabled = "";
    } else {
      singleField.disabled = true;
    }
  }
}

checker.onclick = () => {
  blockFileds();
}

Удалить элементы из функции, И прикрепите addEventListener ко входу

   
        let inputsForm = document.getElementsByClassName('block');
        let checker = document.getElementById('scale1');
        function blockFileds() {
            for (let singleField of inputsForm) {

                if (checker.checked) {
                    singleField.disabled = false;

                } else {
                    singleField.disabled = true;
                    
                }
            }
        }

        blockFileds()
        checker.addEventListener("click", (e)=>{
            blockFileds()
        })