With Shopify Classic Customer Accounts, brands could create custom form fields for customers to input upon account creation. This was a useful way to gather customer data and build profiles upon signup. Despite this, Customer Account pages were still pretty basic and didn't display the information that customers input when creating their account.
Many new features and capabilities launched or under development by Shopify don't work with Classic Customer Accounts. To use those features, brands must enable New Customer Accounts.
With New Customer Accounts, brands can't customize the Account Creation page, which only allows customers to input their email address.
However, the new "Customer Profile Page" can be edited, but the only native editable fields are "Name", "Email", and "Address".
Customer Profiles can be customized with Extensions (apps), such as Customer Accounts Pro! Think of Extensions as apps for your Customer Profile Page - which can be browsed in the Shopify App Store. With Customer Fields Pro you can add customer profile fields for customers to input their data in to, so you can collect the data you need for your business that you can no longer collect during account creation.