Twig: Override a view of a particular field (https://symfony.com/doc/current/form/form_customization.html#how-to-customize-an-individual-field)

form.html.twig

{% extends "@app/form_layout.html.twig" %}
{% block _{FORM_NAME}_{ELEMENT_NAME}_widget %}
        {{ form_widget(form) }} Modified
{% endblock %}

For example: A test form type

class TestType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        parent::buildForm($builder, $options);
        $builder
            ->add("field1", "textarea", array("required"=>false))
        ;

    }

    public function getName()
    {
        return "test";
    }
}

could be overridden as such:

{% extends "@app/form_layout.html.twig" %}
{% block _test_field1_widget %}
        {{ form_widget(form) }} modified
{% endblock %}