I found a solution so that ACF creates the correct code from a WYSIWYG field. You only have to add
add_filter( 'acf_the_content', 'wp_make_content_images_responsive' );
to your functions.php. I hope Elliot will add this direct into the code, so that ACF filters the WYSIWYG content like WP does.
For the image field this code works for me:
$image = get_field('my_image');
$img_src = wp_get_attachment_image_url( $image['id'], 'full' ); $img_srcset = wp_get_attachment_image_srcset( $image['id'], 'full' ); ?>
<img src="<?php echo esc_url( $img_src ); ?>"
width = "<?php echo $image['sizes']['Stripe-width']; ?>"
height = "<?php echo $image['sizes']['Stripe-height']; ?>"
srcset="<?php echo esc_attr( $img_srcset ); ?>"
sizes="(max-width: 100vw) 480px" alt="<?php echo $image['alt']; ?>"
>
