Add to cart button not displaying inside custom text in drupal 8 views
AFAIK you can't rewrite the output of rendered entities (add to cart form) with replacement patterns for in D8 views.
I ran into this same problem and discussed it with the maintainer of the commerce_variation_cart_form module. You can read about it here: https://www.drupal.org/project/commerce_variation_cart_form/issues/3081903
Specifically this from comment #17 https://www.drupal.org/project/commerce_variation_cart_form/issues/3081903#comment-13269416

All the render code runs including the form generation and extra field addition, but anything in a views field rewrite is then run through Xss::filterAdmin() to remove dangerous tags, and apparently form is a dangerous tag