Your description is a bit confusing. Did you encounter an error when configuring the newly installed SSRS? Or have some operations been performed that caused errors in SSRS that was originally running normally? I noticed you mentioned signing up for the Power BI service. Is this error on the SSRS side or on the Power BI side?
According to the search, most of the errors that appear "The report server cannot verify the integrity of the encrypted data in the database" are due to the encryption key. You can refer to this thread: https://stackoverflow.com/questions/46203955/the-report-server-was-unable-to-validate-the-integrity-of-encrypted-data.
Regarding getting this error when registering Power BI, I found this similar thread for you: https://community.fabric.microsoft.com/t5/Service/sql-server-2016-reporting-services-configuration-manager-power/m-p/28021. For more questions about Power BI, you can seek help in the Power BI forum: https://community.fabric.microsoft.com/t5/Power-BI-forums/ct-p/powerbi.
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Best regards,
Aniya