Magento 2 Guest to Customer - Cynoinfotech
https://www.cynoinfotech.com/product/guest-to-customer-magento-2-extension/
Guest to Customer extension developed by Cynoinfotech helps to add a button in "Sales Order View Page" which will create a customer based on the guest order information by sending an email to the guest with email and password details. A guest customer can login as a customer using these details. The Guest to Customer Magento 2 extension converts a guest customer into a registered customer if the guest does not complete a lengthy registration process to create a customer account.