The “register” feature doesn’t appear on my site

For registration and registered users features to be available – such as a users order history page – registrations has to be enabled on your site(s).

To do so go to: WP(WordPress) -> Settings -> General and enable Anyone can register

If you are using a multisite setup you will have to do this in the network settings.

Furthermore, please ensure the dedicated "email" field in Wppizza -> Order Form Settings is enabled and set to be required (to allow the user to receive his/her password for a newly created account)
This is the field that has the hardcoded, non-changeable “Type / Validation” of “email”

Note: the “continue as guest / register” options will only show up if the user is NOT logged in already (for obvious reasons), else a simple checkbox “update my details” will be displayed.