You can choose to save the database structure to a snapshot file before comparing and synchronizing the database schema. To do this, check Take a snapshot of the database before synchronization, and then specify a snapshot file.
Below is the xml fragment generated when you choose to save the database to a snapshot file.
<RightDatabase><SqlServer>DEVSRV003\SQL2019</SqlServer><DatabaseName>AdventureWorks</DatabaseName><TrustedConnection>true</TrustedConnection><SaveToSnapshotFile>D:\QA\Idera\SqlSchema\Snapshots\AdventureWorks.snpx</SaveToSnapshotFile></RightDatabase>