Hi @Fred Schmid
I created the same environment as you, and when I access the Web Service URL and Web Portal URL, I don't get the error you mentioned.
Based on my search, if there is an authentication setting conflict between the report server Web.config file and the RSReportServer.config file, HTTP 401 and HTTP 500 errors are generated. For more details, you can refer to this link: https://learn.microsoft.com/en-us/previous-versions/sql/sql-server-2008-r2/ms159778(v=sql.105).
If the link I provided for you doesn't work, perhaps you can use the phone service to check your server status more closely and usually solve your problem.