If that’s the case then it sounds like it might not be possible. I’m not sure if this is a protocol limitation or a feature limitation, but you are free to create a feature request here if you would like.
To summarize for future users, the requirement here is to populate a login hint for a SAML connection, with Okta as IDP. The Auth0 docs state that this isn’t possible because of the SAML connection, as some IDPs don’t support login hint. I looked through the Okta docs and can’t find anything about supporting it.
This would sometimes be possible by passing params upstream.