Power BI report server: Login failed for user 'NT AUTHORITY\ANONYMOUS LOGON' when trying to view a report
Not familiar with virtual service accounts, but this is often related to Kerberos authentication.
Try using Microsoft® Kerberos Configuration Manager for SQL Server® to see if it can generate the SPNs for you.
It's a rather easy to use tool from Microsoft which will detect your SPN settings, and create scripts you can execute to fix your issues.