If the trigger to the Flow/Workflow is from the Portals you are better off with a Workflow (Real-time). The reason here is because power automate flows are always Async, and your Portals won't have visibility of the new created record once the flow is finished, you will end up with caching issues, possibly having to wait 15min to view the record in the Portal.
There are a few options to load your new created record, probably the easiest would be after the workflow you can redirect to a web page, containing a list of cases, you can even create a different entity list showing only "cloned cases"
Another option would try to perform a retrieve to get the new created record, you need to find the correct filter criteria to get the correct record, and then redirect via JS to the entity form page