Hey @datewithpride !
If you are hard coding these fields directly into your theme, such as with Shopify’s guide (https://shopify.dev/docs/themes/customer-engagement/additional-customer-information), these extra fields generally get stored directly in the customer account’s note section.
The alternative option to this would be using an app such as Helium Customer Fields which gives you a no-code way to build and install a custom registration form, and saves the information directly into customer metafields, which is generally a lot more useful than using the note section.