On the day when synthetic full backup is scheduled, Veeam Backup & Replication triggers a new backup job session.
During this session, Veeam Backup & Replication first performs incremental backup in a regular manner and adds a new incremental restore point to the backup chain.
VM data for this incremental restore point is retrieved from the production storage. Incremental backup helps Veeam Backup & Replication ensure that the synthetic full backup scheduled on this day includes the latest changes of the source VM in the production environment.
At the end of the backup job session, the Veeam Data Mover Service in the backup repository builds a new synthetic full backup using restore points that are already available in the backup chain, including the newly created incremental restore point.