We also have a separate Magento 2 Custom Registration Fields module that allows the admin to create custom fields for customers. Henceforth, you can extend your customer sign-up form using the Custom Magento 2 attribute module. For more information, you can check it on our store. if you want to know How to create a Customer Custom attribute in Magento 2, read this blog.

https://webkul.com/blog/how-to-creat...n-magento-2-0/