Hi
Based on my test, we are able to connect to SSRS web portal use web data source in Power BI desktop. But report data can't be retrieved, it only gets HTML elements.
You need to connect to the data source which is the same as the one in SSRS report. Or you can try to pin SSRS visuals to Power BI Service, see: Pin Reporting Services items to Power BI Dashboards.
Best Regards,
Qiuyun Yu