Simplified Drupal config forms since Drupal 10.2

NewSettingsForm.php

<?php declare(strict_types = 1);

namespace Drupal\my_module\Form;

use Drupal\Core\Form\ConfigFormBase;
use Drupal\Core\Form\FormStateInterface;
use Drupal\Core\Form\RedundantEditableConfigNamesTrait;

/**
 * Configure mymodule settings for this site.
 */
final class MyModuleSettingsForm extends ConfigFormBase {

  use RedundantEditableConfigNamesTrait;

  /**
   * {@inheritdoc}
   */
  public function getFormId(): string {
    return 'my_module_settings';
  }

  /**
   * {@inheritdoc}
   */
  public function buildForm(array $form, FormStateInterface $form_state): array {
    $form['example'] = [
      '#type' => 'textfield',
      '#title' => $this->t('Example'),
      '#config_target' => new ConfigTarget(
        'mymodule.settings',
        'example',
        toConfig: static::class . '::normalize'
      ),
    ];
    return parent::buildForm($form, $form_state);
  }
  
  /**
   * This example callback modifies the config value before it is stored (toConfig).
   */
  public static function normalize(string $value): string {
    return mb_strtoupper(trim($value));
  }

}