Can't load reportserver in browser
The issue is most likely that you haven't configured your Service Principal Names for the Report Server, so it is encountering an error trying to utilise Kerberos Authentication.
Firstly, you need to confirm your SPNs are configured correctly for the Report Server. You can use Kerberos Configuration Manager for SQL Server to identify any issues with your SPNs and fix those issues.
Once your SPNs are corrected, add the address (http://servername/) to your trusted sites to enable your Windows identity to be passed through automatically and facilitate SSO.