1) Do you mean that you want to show add to cart button on hover only? Go to Theme Options > WooCommerce > Shop > Product style and choose the hover effect – Buttons on hover.
2) WooCommerce Product Add-ons plugin generate issue while adding to cart even with the Storefront theme https://prnt.sc/1if4bmx So, contact plugin author to fix the issue. If plugin is disabled add to cart works fine.
3) Min and Max Quantity for WooCommerce plugin generates the error with the Buy now button https://prnt.sc/1if632e Contact plugin author to fix the issue.
