Get unmapped values with Symfony forms

I'm trying to create an API that takes multiple values mapped as parameters, but it's possible that this API takes other values and I need to store this information in my database.

I would like to know how I can get these unmapped values.

My form is basically like this:

<?php

namespace App\ApiController\Integration\Webhook\Proposal;

use Simonetti\MesaCredito\Proposta\Webhook\FinancingDTO;
use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\Extension\Core\Type\CollectionType;
use Symfony\Component\Form\Extension\Core\Type\DateType;
use Symfony\Component\Form\Extension\Core\Type\IntegerType;
use Symfony\Component\Form\Extension\Core\Type\TextType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\OptionsResolver\OptionsResolver;
use Symfony\Component\Validator\Constraints\NotBlank;

class FinanciamentoType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options): void
    {
        $builder
            ->add('amortizationType', TextType::class, [
                'constraints' => [
                    new NotBlank(),
                ],
                'documentation' => [
                    'example' => 'SAC',
                ],
            ])
            ->add('assetValue', IntegerType::class, [
                'required' => true,
                'documentation' => [
                    'example' => 100,
                ],
            ])
            ->add('calculeDate', DateType::class, [
                'required' => true,
                'widget' => 'single_text',
                'input'  => 'datetime_immutable',
                'format' => DateType::HTML5_FORMAT,
            ])
            ->add('notMapped',TextType::class,['mapped'=>true]);
    }

    public function configureOptions(OptionsResolver $resolver): void
    {
        $resolver->setDefaults([
            'allow_extra_fields' => true,
            'data_class' => FinancingDTO::class,
        ]);
    }
}

My FinancingDTO class looks like this:

<?php

namespace Simonetti\CreditDesk\Proposal\Webhook;

class FinancingDTO implements \JsonSerializable
{
    private string $amortizationType;
    private int $assetValue;
    private \DateTimeImmutable $dataCalculo;
    private mixed $notMapped = [];

    public function setAmortizationType(string $amortizationType): self
    {
        $this->amortizationType = $amortizationType;

        return $this;
    }

    public function amortizationType(): string
    {
        return $this->amortizationType;
    }

    public function setAssetValue(int $assetValue): self
    {
        $this->assetValue = $assetValue;

        return $this;
    }

    public function assetValue(): int
    {
        return $this->valorAtivo;
    }

    public function setCalculeDate(\DateTimeImmutable $calculeDate): self
    {
        $this->calculeDate= $calculeDate;

        return $this;
    }

    public function calculeDate(): \DateTimeImmutable
    {
        return $this->calculeDate;
    }

    /**
     * @return mixed
     */
    public function getNotMapped(): mixed
    {
        return $this->notMapped;
    }

    /**
     * @param mixed $notMapped
     */
    public function setNotMapped(mixed $notMapped): self
    {
        $this->notMapped = $notMapped;

        return $this;
    }
}

I want to add the unmapped fields in notMapped Any idea how to solve it?