Sorry. Now its right.
The cartManager's 'createOrderItem'-function was originally called with no quantity value assigned. Which means the
default-value of 1 got applied. (\Drupal\commerce\modules\cart\src\CartManagerInterface)
The patch changes the call of the 'createOrderItem'-function so that the quantity-value of the 'main-variation' is used.
I simply added {{ variation_entity.getPrice|commerce_price_format }} to
commerce-pado-addon-product-variation-label.html.twig:
/**
* @file
* Default product add-on add product variation label template.
*
* Available variables:
* - variation_entity: The add on product.
*
* @ingroup themeable
*/
#}
Add {{ variation_entity.label }} {{ variation_entity.getPrice|commerce_price_format }}
Same Problem in 2023.
Is there a solution for this problem after all this years?