We have configured Stretched Cluster, which we have tested to turn off an entire datacenter and the VMs were moved to the Secondary Site but at the time of testing the VMs were restarted and it took two minutes to complete the entire process.
I have a question if it is possible to have zero downtime of the VMs if one of the sites goes down and the VMs must be moved to the active site,
I will appreciate if you can clarify the doubt
what you're asking for is named Fault Tolerance VMs.
AFAIK it's not supported in combination with vSAN stretched Cluster, but I'm happy to get corrected.
As an Fault Tolerance protected VM requires another "shadow" VM which is in sync (Files & Disk, RAM Content, CPU Registers...) that feature does really require a superfast and low latency link between the nodes which would host those paired VMs.