i want to populate second combo box based on valure selected in first combo- both the combo box values will be retrieved from database using php

<div class="col-12"><br>
    <label class="form-label">Category*</label>                        
    <select class="form-control" name="category" id="category">
        <option disabled="disabled" selected="selected">Choose option</option>
        
<?php
    $q="SELECT DISTINCT category FROM `categorylist` ORDER BY category asc"; 
    $r = mysqli_query($connection, $q);     
    while ($row = mysqli_fetch_array($r)) { 
        $dropdown=$row['category'];
        echo "<option value='$dropdown'>$dropdown</option>"; 
    } 
?>
        
    </select>
</div>  
<div class="col-12"><br>
    <label class="form-label">subCategory*</label>                        
    <select class="form-control" name="subcategory" id="subcategory">
    
        <option disabled="disabled" selected="selected">Choose option</option>
        
<?php
    $q1="SELECT DISTINCT subCategory FROM `categorylist` ORDER BY subCategory asc"; 
    $r1 = mysqli_query($connection, $q1);     
    while ($row = mysqli_fetch_array($r1)) { 
        $dropdown=$row['subCategory'];
        echo "<option value='$dropdown'>$dropdown</option>"; 
    } 
?>
        
    </select>

source https://stackoverflow.com/questions/70137004/i-want-to-populate-second-combo-box-based-on-valure-selected-in-first-combo-bot