In bootstrap 4 these classes were working fine. But they are not working in Bootstrap 5. Any idea why?

Note: d-block d-lg-flex , text-center text-lg-start text-md-end these are working fine. Looks like just margin and padding related classes are not working.

Sample code:

 <div class="d-block d-lg-flex justify-content-center flex-row bd-highlight ">
    <div class="mb-0 mb-md-3 mb-lg-0">
        <div class="dropdown text-center cairo ">
            <select x-model="selectedUnits" class="form-select feature_text" aria-label="Default select example">
                <option selected="" disabled="">Select unit amount</option>
                <option value="myval">1 unit</option>
                <option value="myval">1 unit</option>
                <option value="myval">1 unit</option>
            </select>
        </div>
    </div>
</div>