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.