BUG or what?

sure.

let currentTable := tableId(this);
if currentTable = "RC" then
    let HR := cnt(select Album where Genres like "Hard Rock");
    html("
    <script>
      var HR = '" +
    HR +
    "';
      var fields = document.querySelectorAll('label');
      fields.forEach(function (field) {
        if (field.innerText === 'Hard Rock') {
          field.style.fontFamily = 'Verdana';
          field.style.fontSize = '10px';
          field.style.color = 'black';

      var currentField = field.nextElementSibling;
      currentField.textContent = HR;
      currentField.style.border = '2px solid red';
      currentField.style.padding = '2px';
      currentField.style.background = 'radial-gradient(circle, red 30%, white)';
      currentField.style.width = '120px';
      currentField.style.height = '120px';
      currentField.style.textAlign = 'center';
      currentField.style.lineHeight = '120px';
      currentField.style.fontFamily = 'Helvetica';
      currentField.style.fontSize = '22px';
      currentField.style.color = 'white';
      currentField.contentEditable = true;
    } else {
      var currentField = field.nextElementSibling;
      currentField.style = ''; // Rimuove eventuali stili applicati precedentemente
    }
  });
</script>
")
end

this script is assigned to the formula itself. To prevent this behavior I am now going to create a new formula field that refers to the field labelled "Hard Rock", but in this case it will be not a formula but a normal field

unfortunately not, I will try something new inn these days

Sean thank you for all your effort! I'll write here if something get better

oh I almost forgot Sean: excellent choice of Hard Rock and Progressive Rock in your test database!

this is associated to the formula field called "genre not Assigned". 

let TE := cnt(select Album where Genre = null);
html("<button id='button1'>" + TE +
"</button><meta charset='utf-8'/><meta name='viewport' content='width=device-width, initial-scale=1'>

<style>
    body {
        display: flex;
        justify-content: center;
        align-items: center;
        height: 100vh;
        margin: 0;
        background-color: #f7f7f7;
    }

    button {
        border: none;
        background-color: orange;
        background: radial-gradient(circle, orange 30%, white);
        border: 2px solid orange;
        padding: 2px;
        width: 120px;
        height: 120px;
        text-align: center;
        line-height: 120px;
        font-family: Helvetica;
        font-size: 22px;
        color: white;
        outline: none;
        cursor: pointer;
        border-radius: 5px;
    }
      </style>")

added this to onclick action:

openTable("Album", "GenreNull")

obviously I created a new view of Table Album with the genre criteria on it.

I don't know if I understood well what you are saying, if not sorry, my English is not so good