gistfile1.txt

<?php
/*
Plugin Name: Custom Unpublish Tool
Description: Add an Unpublish tool with a date picker in the Gutenberg editor.
*/

// Enqueue the date picker script
function custom_unpublish_enqueue_scripts() {
    wp_enqueue_script('jquery-ui-datepicker');
}
add_action('enqueue_block_editor_assets', 'custom_unpublish_enqueue_scripts');

// Add custom Unpublish tool
function custom_unpublish_tool() {
    $post = get_post();
    $unpublish_date = get_post_meta($post->ID, '_unpublish_date', true);
    ?>
    <div class="unpublish-tool">
        <label for="unpublish-date">Unpublish Date:</label>
        <input type="text" id="unpublish-date" name="unpublish-date" value="<?php echo esc_attr($unpublish_date); ?>" />
    </div>
    <script>
        jQuery(document).ready(function($) {
            $('#unpublish-date').datepicker({
                dateFormat: 'yy-mm-dd',
                changeMonth: true,
                changeYear: true
            });
        });
    </script>
    <?php
}
add_action('admin_enqueue_scripts', 'custom_unpublish_enqueue_scripts');
add_action('edit_form_after_title', 'custom_unpublish_tool');

// Save Unpublish date
function custom_save_unpublish_date($post_id) {
    if (isset($_POST['unpublish-date'])) {
        update_post_meta($post_id, '_unpublish_date', sanitize_text_field($_POST['unpublish-date']));
    }
}
add_action('save_post', 'custom_save_unpublish_date');