使用XAMPP在文件中使用$ _POST时出现问题

I want to process form input into a MYSQL database but I am having trouble getting other files to recognize data in the _POST array and keep getting the typical "Undefined index" error. My form:

    <?php
    $category = '';
    $item = '';
    // Check if form is posted
    if (isset($_POST['item'])){
        // Declare POST'd values into variables
        $category = $_POST['Category'];
        $item = $_POST['item'];
    }
    ?>
    <!-- Item Input form -->
    <form id='additem' method='post' action="">
    <fieldset>
        <legend>Add Item</legend>
        <table>
        <tr>
            <td><label for='Category'>Category: </label></td>
            <td><input type='text' name='Category' list='categories' value='<?php $category;?>' /></td>
                <datalist id='categories'>
                    <option value='Protein'>
                    <option value='Produce'>
                    <option value='Baked Goods'>
                    <option value='Dry/Canned'>
                    <option value='Household'>
                </datalist>
        </tr><tr>
            <td><label for='item'>Name: </label></td>
            <td><input type='text' name='item' value='<?php $item;?>' /></td>
        </tr><tr>
            <td></td><td><input type='Submit' value='Submit' /></td>
        </tr>
        </table>
    </fieldset>
    </form>

When I use $_POST in this file, it works perfectly fine but when I try to use it in another file, process.php:

<?php
echo $_POST['Category'];
echo '<br>';
echo $_POST['item'];
?>

it gives: Notice: Undefined index: Category in E:\Documents\XAMPP\htdocs\Website\process.php on line 3 Notice: Undefined index: item in E:\Documents\XAMPP\htdocs\Website\process.php on line 5

Now I know my _POST array is not empty, because I can access it within my original form file. If I change the form action to "process.php" it works, but also automatically takes me to that page. What I want is for process.php to send data to my database while the form returns to its own page ready for more input. I have even literally copy and pasted the code from that example into files and attempted to run those, but I get similar errors so I think it might be an issue with XAMPP/Apache.

To address this, I have also tried this but post_max_size was already set to 8M, and as per another post I saw somewhere I added 'variables_order = "EGPCS"' in the line below. Still I am getting the same undefined index.

Is there something wrong with my code? Is it XAMPP/Apache? I have tried fresh installing XAMPP, but the issue still persists.