You need to set a watcher on all accordion items and check if any of them are open.

If none is open then open the first one.

$('#accordion-id .collapse').each((i, e) => 
    $(e).on('hidden.bs.collapse', () => {
        // check if an accordion item is expanded
        let isExpanded = false;
        $('#accordion-id [aria-expanded]').each((i, element) => {
            if ($(element).attr("aria-expanded") === 'true') {
                isExpanded = true;
            }
        });
    
        // show the first accordion item
        if (!isExpanded) {
            $('#btn-firs-accordion-id').click();
        }
    })
);

I found a solution for the Bootstrap 4 versione but none for Bootstrap 5.

After a while I was able to solve the problem with this code:

<script>
const accordions = document.querySelectorAll(".accordion-collapse");
let opening = false;
accordions.forEach(function (el) {
  el.addEventListener("hide.bs.collapse", (event) => {
    if (!opening) {
      event.preventDefault();
      event.stopPropagation();
    } else {
      opening = false;
    }
  });
  el.addEventListener("show.bs.collapse", (event) => {
    opening = true;
  });
});
</script>

I'm not an expert js developer so I know it's not the most elegant solution but at least it solved my issue.