Access the Admin Portal

There is no separate admin portal with metrics for the on-prem Power BI Report Server. If you want execution metrics you can build your own reports or data model over the execution log view see https://docs.microsoft.com/en-us/sql/reporting-services/report-server/report-server-executionlog-and-the-executionlog3-view?view=sql-server-ver15

We have our own ETL process which pulls this information into a separate database since the execution log only retains the data for something like 90 days and we did not want to bloat the size of the ReportServer database.