By design, SCIM-provisioned users cannot be edited once they have been created.
SCIM-provisioned users can only authenticate using Office 365 or OKTA, as these are the only two currently supported methods for SCIM. With that in mind, best practice is to decide which authentication method to use during SCIM setup as this cannot be changed later.
A later product version may allow additional authentication methods for SCIM-provisioned users (e.g. ADFS). At present, if portal users need to use ADFS, their accounts need to be created manually.