RE: Portal search functionality
Hi Justin,
You could pay attention to the following part of the article.

The default filter for cases in portal is status=resolved and publish to web=true.
So you could try to find a resolved case and open your case form in D365 and set the "publish to web" as true.

And then I could find my case in portal.

Please note that we could not search for key words like "test" or "case", we should follow the rules like "test*" and "*case" or just the fullname.
If you want to change the filter of the case searching, you could go to D365 case view and find a view named "portal search", then change the filter condition of it and publish, but there is also an important thing that if we clear all the conditions we will be able to search the case in portal but we may not be able to open the detail form cause the portal will give an error message of permission error. I haven't found how to fix it yet :(. Microsoft says that we should update the custom-service case web template appropriately but there is no sample about how to change it.
You could find the information in the following article "Entity-specific handling" part.
https://docs.microsoft.com/en-us/dynamics365/customer-engagement/portals/search
Hope it helps.
Best Regards,
Leo