How do I create an overview page with custom calculations from a post-type?

It seems you are asking for a complete custom funcionality,

To add menu, you can use this.

function wpdocs_register_my_custom_menu_page() {
    add_menu_page(
        __( 'Custom Menu Title', 'textdomain' ),
        'custom menu',
        'manage_options',
        'myplugin/myplugin-admin.php',
        'custom_callback_function',
        plugins_url( 'myplugin/images/icon.png' ),
        6
    );
}
add_action( 'admin_menu', 'wpdocs_register_my_custom_menu_page' );

function custom_callback_function(){

echo 'Here is my page contents';

}

https://developer.wordpress.org/reference/functions/add_menu_page/

You can use $wpdb query class for custom functionalities

https://codex.wordpress.org/Class_Reference/wpdb

Hopes this will give you basic idea about this.