The dropdown menu is not expanding. CSS and JS are connected correctly

I am a beginner in web development. I need some help. The dropdown menu is not expanding. CSS and JS are connected correctly. What could be the reason?

I checked the CSS/JS classes and connected files. Everything seems to be correct, I even used GPT, but no results. 🙁 I can provide other project files if needed. Here is the code from the main file layout.html.

{% load static %}
<!DOCTYPE html>
<html lang="uk">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>{% block title %}Головна{% endblock %}</title>
    <link href="https://stackpath.bootstrapcdn.com/bootstrap/5.1.3/css/bootstrap.min.css" rel="stylesheet">
    <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.5.2/css/bootstrap.min.css">
    <link rel="stylesheet" href="{% static 'main/css/main.css' %}">
    <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/5.15.4/css/all.min.css">
    <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/fullcalendar/5.10.1/main.min.css">
</head>
<body>
    <button class="btn btn-primary" id="sidebarToggle">
        <i class="fas fa-bars"></i>
    </button>
    <div class="d-flex">
        <aside class="flex-shrink-0 p-3 bg-dark text-white sidebar" id="sidebar">
            <a href="/" class="d-flex align-items-center mb-3 mb-md-0 me-md-auto text-white text-decoration-none">
                <img src="{% static 'main/img/2.png' %}" alt="Logo" class="small-logo">
            </a>
            <hr>
            <ul class="nav nav-pills flex-column mb-auto">
                <li class="nav-item">
                    <a href="{% url 'layout' %}" class="nav-link text-white {% if request.resolver_match.url_name == 'layout' %}active{% endif %}" aria-current="page">
                        <i class="fas fa-heart"></i> Головна
                    </a>
                </li>
                <li>
                    <a href="{% url 'staff' %}" class="nav-link text-white {% if request.resolver_match.url_name == 'staff' %}active{% endif %}">
                        <i class="fas fa-users"></i> Особовий склад
                    </a>
                </li>
                <li>
                    <a href="{% url 'calendar' %}" class="nav-link text-white {% if request.resolver_match.url_name == 'duty' %}active{% endif %}">
                        <i class="fas fa-list"></i> Подати наряд
                    </a>
                </li>
                <li>
                    <a href="{% url 'profile' %}" class="nav-link text-white {% if request.resolver_match.url_name == 'profile' %}active{% endif %}">
                        <i class="fas fa-user"></i> Профіль
                    </a>
                </li>
                <li>
                    <a href="{% url 'calendar' %}" class="nav-link text-white {% if request.resolver_match.url_name == 'calendar' %}active{% endif %}">
                        <i class="fas fa-calendar"></i> Календар
                    </a>
                </li>
            </ul>
            <li class="nav-item">
                <a class="nav-link dropdown-toggle text-white" href="#" id="dropdownMenuLink" data-bs-toggle="dropdown" aria-expanded="false">
                    Dropdown
                </a>
                <ul class="dropdown-menu" aria-labelledby="dropdownMenuLink">
                    <li><a class="dropdown-item" href="#">Action</a></li>
                    <li><a class="dropdown-item" href="#">Another action</a></li>
                    <li><a class="dropdown-item" href="#">Something else here</a></li>
                </ul>
            </li>
        </ul>
        
        </aside>
    <script src="https://code.jquery.com/jquery-3.6.0.min.js"></script>
    <script src="https://cdn.jsdelivr.net/npm/@popperjs/[email protected]/dist/umd/popper.min.js"></script>
    <script src="https://stackpath.bootstrapcdn.com/bootstrap/5.1.3/js/bootstrap.min.js"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/fullcalendar/5.10.1/main.min.js"></script>
    <script src='https://cdn.jsdelivr.net/npm/@fullcalendar/[email protected]/index.global.min.js'></script>
    <script src='https://cdn.jsdelivr.net/npm/@fullcalendar/[email protected]/index.global.min.js'></script>
    <script src='https://cdn.jsdelivr.net/npm/@fullcalendar/[email protected]/index.global.min.js'></script>
    <script>
        document.getElementById('sidebarToggle').addEventListener('click', function () {
            document.getElementById('sidebar').classList.toggle('active');
            this.classList.toggle('active');
        });

        document.addEventListener('DOMContentLoaded', function() {
            var calendarEl = document.getElementById('calendar');
            if (calendarEl) {
                var calendar = new FullCalendar.Calendar(calendarEl, {
                    initialView: 'dayGridMonth',
                    locale: 'uk',
                    editable: true,
                    selectable: true,
                    events: '/get_duties/',  // Завантаження нарядів з сервера
                    select: function(info) {
                        var dutyDateInput = document.getElementById('dutyDate');
                        dutyDateInput.value = info.startStr;
                        var dutyFormModal = new bootstrap.Modal(document.getElementById('dutyFormModal'));
                        dutyFormModal.show();
                        calendar.unselect();
                    },
                    eventClick: function(info) {
                        if (confirm('Ви впевнені, що хочете видалити цю подію?')) {
                            $.ajax({
                                type: 'POST',
                                url: '{% url "delete_duty" %}',
                                data: {
                                    'id': info.event.id,
                                    'csrfmiddlewaretoken': '{{ csrf_token }}'
                                },
                                success: function(response) {
                                    if (response.status === 'success') {
                                        info.event.remove();
                                    } else {
                                        alert('Сталася помилка при видаленні наряду.');
                                    }
                                },
                                error: function(response) {
                                    alert('Сталася помилка при видаленні наряду.');
                                }
                            });
                        }
                    }
                });
                calendar.render();
            }

            $('#dutyForm').on('submit', function(event) {
                event.preventDefault();
                $.ajax({
                    type: 'POST',
                    url: $(this).attr('action'),
                    data: $(this).serialize(),
                    success: function(response) {
                        $('#dutyFormModal').modal('hide');
                        calendar.refetchEvents();
                    },
                    error: function(response) {
                        var errors = response.responseJSON.errors;
                        var errorMessage = 'Сталася помилка при подачі наряду:n';
                        for (var field in errors) {
                            errorMessage += field + ': ' + errors[field].join(', ') + 'n';
                        }
                        alert(errorMessage);
                    }
                });
            });
        });
    </script>
</body>
</html>