SSRS error "something went wrong please try again later" in web portal

I have a brand new installation of SQL Server Reporting Services 2019 on top of MSSQL 2019 Enterprise CU1. SSRS has been installed and configured using default settings, apart from the service account it should use. Both AD and MSSQL instance are configured in minimum permissions only (or close to this state). When I am accessing the Web Portal I receive an error saying "please try again later", which isn't much of help. I found many similar posts asking for help on the same issue, but wanted to see the answer here.