POST to /u/signup/identifier redirects to /u/login/password when entering an email address with the domain listed for Home Realm Discovery(HRD) on Azure AD Enterprise Connection. We expect it redirected to https://login.microsoftonline.com/
This is due to a product issue. We have a backlog item for it.
A temporary workaround is the following.
Create a SAML or OIDC Enterprise connection to your Azure AD tenant instead. When clicking on signup and entering an email address with a domain used for HRD using any of those connections, the user will be redirected to the IdP login page as expected.
Please note that with the Azure AD connections, you have the option to verify the user’s email, but it is not possible with other Enterprise connections.