Hi Sudhakar P,
Thank you for reaching out and posting the query.
When backing up SQL databases in an Azure VM using Recovery Services Vault, there is typically no downtime required for the backup process. Azure Backup is designed to perform backups without impacting the availability of the databases, allowing applications to continue functioning normally during the backup.
I would request you to refer the below mentioned links for more information
https://learn.microsoft.com/en-us/azure/backup/backup-sql-server-azure-troubleshoot
I hope this information helps. Please do let us know if you have any further queries.