Html – Dropdown with Bootstrap not working: the ul list is not dropping down at all?

There are total two dropdowns in my templated, but none of them are working: the one with and without thymeleaf attributes. Didnt tried changing the css properties, because it was working properly before but now it doesnt work at all.

<div class="shop-product-fillter style-2">
                    <div class="totall-product">
                        <p> We found <strong class="text-brand">5   </strong> items for you!</p>
                    </div>
                    <div class="sort-by-product-area">
                        <div class="sort-by-cover mr-10">
                            <div class="sort-by-product-wrap">
                                <div class="sort-by">
                                    <span><i class="fi-rs-apps"></i>Show:</span>
                                </div>
                                <div class="sort-by-dropdown-wrap">
                                    <span> 50 <i class="fi-rs-angle-small-down"></i></span>
                                </div>
                            </div>
                            <div class="sort-by-dropdown">
                                <ul>
                                    <li><a class="active" href="#">50</a></li>
                                    <li><a href="#">100</a></li>
                                    <li><a href="#">150</a></li>
                                    <li><a href="#">200</a></li>
                                    <li><a href="#">All</a></li>
                                </ul>
                            </div>
                        </div>
                        <div class="sort-by-cover">
                            <div class="sort-by-product-wrap">
                                <div class="sort-by">
                                    <span><i class="fi-rs-apps-sort"></i>Sort by:</span>
                                </div>
                                <div class="sort-by-dropdown-wrap">
                                    <span> High to Low <i class="fi-rs-angle-small-down"></i></span>
                                </div>
                            </div>
                            <div class="sort-by-dropdown">
                                <ul>
                                    <li><a th:href="@{/shop-list-right}">Featured</a></li>
                                    <li><a  th:href="@{/low-price}">Price: Low to High</a></li>
                                    <li><a class="active" th:href="@{/high-price}">Price: High to Low</a></li>
                                    <li><a href="#">Release Date</a></li>
                                    <li><a href="#">Avg. Rating</a></li>
                                </ul>
                            </div>
                            
                        </div>
                    </div>
                </div>