This should not be a problem with Power BI Report Server. I also don't have Power BI Report Server installed, but my subscription works just fine.
According to your error message, this should be an error caused by the database, please check whether your report server instance can connect to the database.
Configure a Report Server Database Connection (Report Server Configuration Manager)
If it is a timeout connection problem caused by too much data, you can refer to this link.
For more details, you can refer to this link: https://social.msdn.microsoft.com/Forums/sqlserver/en-US/37934c15-7128-4130-bb33-509dea58cfea/an-error-occurred-within-the-report-server-database-this-may-be-due-to-a-connection-failure?forum=sqlreportingservices.
If the answer is helpful, please click "Accept Answer" and upvote it. If you have any questions, please feel free to let me know.
Best regards,
Aniya