User login stuck at 'Preparing for first Use'

This login failure can indicate that the user record from the identity provider has changed.  If this is the case, the user record within Domino may need to be manually corrected to ensure that the user information from the identity provider that is populated in keycloak also matches the user record in the mongoDB database in Domino.  

Updating the user record manually in mongo is inherently dangerous as improper manual updates to the mongo database that backs Domino can create a systemwide outage.  It is recommended to log a ticket with Domino Support for assistance if you run in to this issue.