Not sure this is such a complex issue – WP provides an easy hook to control the email sent to the admin – wp_new_user_notification_email_admin
you can read about the parameters here: https://developer.wordpress.org/reference/hooks/wp_new_user_notification_email_admin/
There is a “to” param, which allows you to define the email address to sent to, then it’s just a case of creating an array ( manually or pulled from some editable source ) of the emails you want to send to and then using some logic to connect your specific field values to the email, if/else or switch or array_search.. whatever works really..
Not sure what else you need on this?