Based on https://symfony.com/doc/current/serializer/custom_encoders.html

FormEncoder.php

<?php

declare(strict_types=1);

namespace App\Infrastructure\Serializer;

use Symfony\Component\Serializer\Encoder\DecoderInterface;
use Symfony\Component\Serializer\Encoder\EncoderInterface;

class FormEncoder implements EncoderInterface, DecoderInterface
{
    public const FORMAT = 'form';

    public function decode(string $data, string $format, array $context = []): array
    {
        parse_str($data, $result);

        return $result;
    }

    public function supportsDecoding(string $format): bool
    {
        return self::FORMAT === $format;
    }

    public function encode(mixed $data, string $format, array $context = []): string
    {
        return http_build_query($data);
    }

    public function supportsEncoding(string $format): bool
    {
        return self::FORMAT === $format;
    }
}