Generally these informations are not published publicly. If you/your customer is keen to know more about it, suggest kindly reach out to the AWS Compliance team AWS Compliance
Am sure, there would be certain information shared directly using this NDA route
IF you think of an AZ as a Datacenter, or multiple DCs within 10-20 miles of each, I would consider a region separation of about 100 miles. You can stretch a VMC cluster across multiple AZs in the same region. If you want to protect yourself against a region failure, you'll need to setup another cluster in another region and look at SRM.
Vmware cloud on AWS is Vmware SDDC software stack (Vsphere | NSX | VSAN) running on AWS hardware.
AWS has a concept of Regions and AZ. AZs are like datacenters in a particular region. Fore more details please refer - Global Cloud Infrastructure | Regions & Availability Zones | AWS
AWS doesn't publish the location of these datacenters. However, AZs are located within a region.
Asia Pacific has a Mumbai region.
and that region has 2 AZs aka Data centers. So you can imagine that these 2 Data centers wouldn't be very far off.
For exact details on the distance between 2 AZs, you would need to reach out to AWS (assuming they publish that data to you under NDA)