This feature was available before Aria Suite Lifecycle 8.18.
However, post upgrade to 8.18, it does not work.
Aria Suite Lifecycle 8.18
This was introduces as a feature change on the product level to accommodate user environments where they do not have any ports opened to the vCenter servers where the cloud proxies are deployed.
This is an expected behavior. Witness and Cloud Proxies will not be snapshotted anymore starting vRLCM 8.18 as they are stateless.
If and when an upgrade fails on cloud proxy, they can be redeployed as needed.
How to take a Snapshot of VMware Aria Operations:
https://knowledge.broadcom.com/external/article?articleNumber=342576