Hello @75969757 , you should be able to use an Azure AD enterprise/SAML application for a Sign-Up User Flow. That being said, Linked-based SSO doesn't provide sign-on functionality through Azure AD. The option simply sets the location that users are sent when they select the application on the My Apps or Microsoft 365 portal. More importantly, LInked-based SSO applications are not SAML applications. You need to create a Azure AD SAML enabled enterprise application or an (OAuth2/OIDC enabled) app registration.
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