Unfortunately the MvcReportViewer does not work with asp.net core. It internally hosts the webform control and calls it’s render. As webform controls are not supported on core this will not work.
To host type the SSRS control, you need a 4.* website. The asp core site can use an iframe or link to the SSRS site.
It should be possible to update the MvcReportViewer to proxy a call to the SSRS site instead of hosting the actual control.