The solution is right in the documentation
but if you miss it, the errors are not too helpful.
You get a servlet error
An unexpected servlet error was encountered.
Please check the log file for more details.In the log file
you will see the following:
06/11/22 09:43:41 portal: [module=PortalServlet, ecid=92635952220,1] ERROR: oracle.webdb.repository.service.RepositoryServiceException: Unable to obtain Portal Repository version.
Search all through metalink and on the web and it will likely tell you that your PORTAL schema password is wrong. Well, that might be true, but once you find it isn't wrong, log in as either PORTAL, sys or system and run the following command:
ALTER USER PORTAL_PUBLIC GRANT CONNECT THROUGH PORTAL;
Bounce everything. I'm interested in finding out if this helps anyone. If it does, leave a comment.