Dropdown not working

Dear Community
I have a problem which I hope you can solve.

• ● The Navbar profile picture should provide a dropdown
• ● The Navbar should open up when you click it in mobile version
  

None of the above happen. You can test it out yourself: http://blogg.bplaced.net/

Here is my Navbar code:

<header>
        <!-- Navbar -->
        <nav class="navbar navbar-expand-lg navbar-dark bg-primary fixed-top">
            <div class="container-fluid">
                <button
                        class="navbar-toggler"
                        type="button"
                        data-toggle="collapse"
                        data-target="#navbarExample01"
                        aria-controls="navbarExample01"
                        aria-expanded="false"
                        aria-label="Toggle navigation"
                >
                    <span class="navbar-toggler-icon"></span>
                </button>
                <div class="collapse navbar-collapse" id="navbarExample01">
                    <a class="navbar-brand" href="/">
                        <img src="img/favicon.png" height="30" alt="Logo" loading="lazy"/>
                    </a>
                    <ul class="navbar-nav mr-auto mb-2 mb-lg-0">
                        <li class="nav-item active">
                            <a class="nav-link active" aria-current="page" href="/">Startseite</a>
                        </li>
                        <li class="nav-item">
                            <a class="nav-link" href="registration">Registrieren</a>
                        </li>
                        <li class="nav-item">
                            <a class="nav-link" href="login">Anmelden</a>
                        </li>
                        <li class="nav-item">
                            <a class="nav-link" href="blogs.php">Blogs</a>
                        </li>
                        <li class="nav-item">
                            <a class="nav-link" href="account">Konto</a>
                        </li>
                    </ul>
                    <ul class="navbar-nav d-flex flex-row">
                        <!-- Avatar -->
                        <li class="nav-item dropdown">
                            <a class="nav-link dropdown-toggle" href="#" id="navbarDropdownMenuLink" role="button" data-toggle="dropdown" aria-expanded="false">
                                <img src="https://mdbootstrap.com/img/Photos/Avatars/img (31).jpg" class="rounded-circle" height="22" alt="profile" loading="lazy"/>
                            </a>
                            <ul class="dropdown-menu" aria-labelledby="navbarDropdownMenuLink">
                                <li><a class="dropdown-item" href="account">Mein Profil</a></li>
                                <li><a class="dropdown-item" href="settings">Settings</a></li>
                                <li><a class="dropdown-item" href="#">Logout</a></li>
                            </ul>
                        </li>
                    </ul>
                </div>
            </div>
        </nav>
        <!-- Navbar -->
    </header>