Is Shipping Rates Calculator+ compatible with pop-up carts?
On some themes, Shipping Rates Calculator+ will display the shipping widget on pop-up carts, although it depends heavily on the theme layout.
Most complex themes or customized pop-up carts, could not be supported right out-of-the-box.
The app is regularly updated to add new features and adapt it's code to the latest changes on Shopify, so we could add support for more pop-up carts as new themes are published on the theme marketplace.
However, please also note that Shipping Rates Calculator+ has a setting called Drawer and pop-up carts support, that will allow you to disable the widget on other pages different from the cart page. By enabling/disabling this option you can avoid possible issues with unsupported pop-up carts.
You can find it in the Advanced preferences section from the preferences page: