Hi Marek,
This looks like an issue with the configuration of Reporting services, not SCOM.
Have you seen this article: https://learn.microsoft.com/en-us/sql/reporting-services/install-windows/configure-the-report-server-service-account-ssrs-configuration-manager?view=sql-server-ver16
Particularly this part:
I would suggest to follow the typical installation steps for setting up SCOM reporting services: https://learn.microsoft.com/en-us/system-center/scom/deploy-install-reporting-server?view=sc-om-2022