With Veeam 7/8/9 B&R stop to work if you rename server.
To restore functionality you need to change and analyze these register fields putting new server name.
I suggest to eviscerate every single key, could you have more subfolder than in my case
HKLM\SOFTWARE\
Veeam\Veeam Backup and Replication\SqlServerName
Veeam\Veeam Backup Catalog\CatalogSharedFolderPath
HKLM\SOFTWARE\Wow6432Node
\Veeam\Veeam Backup and Replication\SqlServerName
\Veeam\Veeam Backup Catalog\CatalogSharedFolderPath
\Veeam\Veeam Backup Packages\{06C5CCDE-FB93-4566-A13F-75C8A2AFABDC}\{564d7967-2024-de0e-f087-bc2e39fba624}\name
It's important that you will change registry keys that are related to sql istances:
\\HKLM\Software\VeeaM\Veeam Backup Catalog\SqlServerName (Should be local)
\\HKLM\Software\VeeaM\Veeam Backup Reporting\SqlServerName (Should be local)