Cannot get customer custom attribute in Magento 2.4

I have created a customer custom attribute with the above code:

namespace VendorCustomerSetup;

use MagentoCustomerSetupCustomerSetupFactory;
use MagentoFrameworkSetupInstallDataInterface;
use MagentoFrameworkSetupModuleContextInterface;
use MagentoFrameworkSetupModuleDataSetupInterface;
use MagentoEavModelEntityAttributeSetFactory as AttributeSetFactory;

class InstallData implements InstallDataInterface
{

    /**
     * Customer setup factory
     *
     * @var CustomerSetupFactory
     */
    private $customerSetupFactory;

    /**
     * @var AttributeSetFactory
     */
    private $attributeSetFactory;

    private $setup;
    
    public function __construct(
        CustomerSetupFactory $customerSetupFactory,
        AttributeSetFactory $attributeSetFactory
    ) {
        $this->customerSetupFactory = $customerSetupFactory;
        $this->attributeSetFactory = $attributeSetFactory;
    }
    
    public function install(
        ModuleDataSetupInterface $setup,
        ModuleContextInterface $context
    )
    {
        $this->setup = $setup;
        $this->setup->startSetup();
        $this->addCustomAttribute(
            'customer_brand',
            [
                'label' => 'Marca',
                'type' => 'varchar',
                'input' => 'multiselect',
                'source' => VendorCustomerModelAdminhtmlAttributeSourceBrand::class,
                'position' => 1001,
                'visible' => true,
                'required' => false,
                'system' => 0,
                'default' => '0',
                'user_defined' => true,
                'adminhtml_only' => 1,
                'validate_rules' => '[]'
            ]
        );

    }

    private function addCustomAttribute($attrCode, $attrParams) {
        $customerSetup = $this->customerSetupFactory->create(['setup' => $this->setup]);
        $customerSetup->removeAttribute(MagentoCustomerModelCustomer::ENTITY, $attrCode);

        $customerSetup->addAttribute(
            'customer',
            $attrCode,
            $attrParams
        );

        $eavConfig = $customerSetup->getEavConfig()->getAttribute('customer', $attrCode);
        $eavConfig->setData('used_in_forms', ['adminhtml_customer']);
        $eavConfig->save();

        $this->setup->endSetup();

        return $this->setup;
    }
}

And with this code the customer admin form now shows my custom attribute:

But now i want to retrieve this attribute in a view with:

$customer->getCustomAttribute('customer_brand');

But it’s aways returning null.

When i debug the code i cannot see the custom attribute in the customer repository:

How can i get this custom attribute?