Version 7.0 U20, does it has a reporting feature to know how much data was replicated on a daily basis, weekly, or custom period?
You can check if the following reports can meet your requirements:
“Outbound Protection Over Time Report” Page 393
“Protection Over Time by Site Report” Page 394
Zerto Analytics API can also provide you the details about the replication.
If none of them can meet your demand, you can also consider raising a feature request for the report being placed in ZVM GUI: https://www.zerto.com/myzerto/support/feature-requests/