GravityForms filter to allow for grouping select choices into labelled groups using special choice options.

gravity-forms-select-optgroupify.php

<?php
/**
 * Filter for GravityForms to group select field choices by a special "optgroup" choice.
 *
 * Simply add a new choice with a value of 'optgroup' to the dropdown to start a group of options. 
 * All following choices will be grouped under it using its label for the group.
 * Any number of groups can be created, as each optgroup choice will start a new group.
 * Supports field placeholder & ungrouped options, but must be before the first group.
 *
 * This snippet can be added to your theme's functions.php, or a custom plugin.
 *
 * Inspired by https://gist.github.com/codearachnid/a06e13be7f01b81b838c
 *
 * @author  Evan Mattson (@aaemnnosttv)
 */

add_filter('gform_field_content', function ($input, $field) {
    if ('select' !== $field->type
        || ! preg_match('#value=[\'"]optgroup[\'"]#', $input)
        || ! preg_match('#<select[^>]*>(.*)</select>#', $input, $option_matches)
        || ! preg_match_all('#<option.*?/option>#', $all_options_html = $option_matches[1], $option_element_matches)
        || ! ($options = reset($option_element_matches))
    ) {
        return $input;
    }

    $label = '';
    $groups = [];
    foreach ($options as $option) {
        if (preg_match('#value=[\'"]optgroup[\'"][^>]*>(.*)</option>#', $option, $option_matches)) {
            $label = $option_matches[1];
        } else {
            $groups[$label][] = $option;
        }
    }

    $grouped_options = array_map(function ($options, $group_label) {
        $html = join("\n", $options);
        
        return $group_label ? "<optgroup label='$group_label'>$html</optgroup>" : $html;
    }, $groups, array_keys($groups));

    return str_replace($all_options_html, join('', $grouped_options), $input);
}, 10, 2);

This works perfectly for Dropdown field but doesn't work for Product Field with Field type set to Dropdown. Please can this be done to work with product field with a dropdown field type