Hi,
The add to cart legacy setting has been removed in the 4.4.0. So what you did won't work when you update your HikaShop.
Now, if the "quantity input" setting set to "none" doesn't work for you, it's either a bug of your version of HikaShop, and thus, when you update, you'll just have to revert your changes, or it comes from some customized view override you already had, which was based on an old version of HikaShop, not supporting that "quantity input" setting, and in that case you'll nee to check your overrides.