Hello,
For Mini Cart, the possible options are under WoodMart >> Header Builder >> Cart element: https://postimg.cc/xqfxv7Bd
And for the cart page, you are right, we used the shortcode of the cart page to fetch the default WooCommerce Cart page, and that is the default, so you can not customize it with the builder directly.
And I have checked too the behavior of the checkout button in the mini cart and on the cart page, it works fine, its normal working is to redirect to the checkout page, which is normally working fine. If you wish to change this behavior, then you should use some Custom Code as this is the default WooCommerce behavior.
Best Regards,