Enabling Multiple Custom Selects Added via Ajax/Fetch in vanilla JS

I have multiple custom select drop downs in my app on screen at any given time. I ALSO inject new rows of content which contain more instances of these custom selects. However, anything loaded in via Fetch/AJAX is not working, obviously since those custom selects were not part of the original element list at runtime.

How can I modify this javascript to cater to both the custom selects on page load, PLUS any new ones added dynamically after the page loads?

let custom_selects = document.querySelectorAll(".custom-select");
custom_selects.forEach(element => element.addEventListener('click', e => {

  // DO NOTHING IF DISABLED
  if (element.disabled) return false;

  // TOGGLE ACTIVE CLASS TO HIDE/SHOW DROPDOWN
  element.classList.toggle('active');

  // SET VARS
  let choose = element.querySelector(".custom-select-choose");
  let hidden_value = element.querySelector("input");

  // IF CLICKING AN OPTION
  if (e.target.matches("li")) {

    // SET THE VARS
    let select_text = e.target.innerText;
    let select_value = e.target.dataset.value;

    // UPDATE WHAT'S DISPLAYED
    choose.textContent = select_text;

    // UPDATE THE HIDDEN INPUT
    hidden_value.value = select_value;
  }

}))

And this is the js that inserts a new row into my page…

///////////////////////
// ADD NEW LINE ITEM //
///////////////////////

if (e.target.matches('#new-line-item')) {

    // GET THE ID OF CURRENT PROJECT OFF THE BUTTON
    let project_id = e.target.dataset.project;
            
    // INSERT AND RETURN THE EMPTY LINE ITEM            
    fetch(project_id+"/cost-add", { headers: {"X-Requested-With": "XMLHttpRequest", 'Content-Type': 'application/x-www-form-urlencoded'}})
        .then(response => response.json())
        .then(function(data) {
            if (data.status == "success") {
            // ADD NEW LINE TO FORM
                e.target.insertAdjacentHTML('beforebegin', data.html);
            }
            // IF ERROR, DISPLAY
            else {
                error_in_results(data.html);
            }
        });

    e.preventDefault();
    e.stopPropagation();

}

Any help or advice is greatly appreciated.