Experience Cloud: Roles are not created as expected when enabling the first external user on an account.

When the First External User Is Enabled

When the "Minimize the number of roles created" setting is enabled under Sharing Settings, enabling the first Active external user on an account creates only a single role using the following format:
<Account Owner Alias> Customer Person Account
The Account Owner Alias corresponds to the Alias field of the user set as the Owner of the account.

When the Second External User Is Enabled

Only when the second Active external user is enabled on the same account does Salesforce create the full number of roles specified in Setup > Digital Experiences > Settings (for example, <Account Name> Customer User). Once these roles are created, all users — including the first Active external user — are reassigned to these new roles.
For more details on role creation behavior when the second external user is created (or when this setting is disabled), see: Experience Cloud: Roles automatically created for accounts when enabling external users (customer or partner)

Purpose of the Minimize Roles Setting

The purpose of this feature is to improve org performance by preventing the creation of unnecessary role hierarchies for accounts that have only one external user.

How to Disable This Behavior

If you want roles to be created immediately when the first external user is enabled, navigate to Setup > Sharing Settings and deselect "Minimize the number of roles created, which improves performance by cutting down processing loads."
Note: Once disabled, the full number of roles specified in your Digital Experience settings will be created for every account as soon as a single external user is enabled. Inactive users are excluded from the count when determining role creation and assignment.