Event doesn't render in FullCalendar v5 with eventRender. What to use instead?

I am trying to render events in FullCalendar v5 through a JSON array but I realised that eventRender does not work for v5. How can I do it instead then? (I do know about event render hooks but didn't understand how to use that)

                <script>
                document.addEventListener('DOMContentLoaded', function() {
                    var calendarEl = document.getElementById('calendar');
                    <?php
                    include 'config.php';
                    $items = array();
                    $query = mysqli_query($connection, "SELECT * FROM events_table WHERE grade_id = '{$studentGradeId}' ");
                    while ($result = mysqli_fetch_array($query)) {
                        $items[] = array(
                            'title' => $result['event_title'],
                            'start' => date('Y-m-d', strtotime($result['event_date'])),
                        );
                    };
                    ?>
                    var items = <?php echo json_encode($items); ?>

                    var calendar = new FullCalendar.Calendar(calendarEl, {
                        initialView: 'dayGridMonth',
                        headerToolbar: {
                            left: 'prev,next today',
                            center: 'title',
                            right: 'dayGridMonth,dayGridWeek,dayGridDay'
                        },
                        events: items,
                        eventrender: function(event, calendarEl) {
                            calendarEl.find('.fc-title').text(event.title);
                        }

                    });
                    calendar.render();
                });
            </script>

from Event doesn't render in FullCalendar v5 with eventRender. What to use instead?