Don´t send email new user

Since Appian 20.3, the Create User smart service has a "Send Account Creation Email" node input that's precisely for that purpose

In the past i've done this by utilizing the "Create User with i18n" smart service contained in the Personalization Utilities plug-in; it's intentionally set up to not send an email out when the account is created (it also allows you to procedurally generate a strong "junk" password to assign to the user as their permanent password upon creation, which must be done even though SSO users will never actually use their password).

Edit: and, the option Carlos mentioned before I managed to submit the reply I was still typing, which might be better if you don't want to use a plug-in.  I'm not sure I actually knew about that one yet.