Ask HN: How do “private cloud” SaaS solutions work?

It seems like companies that traditionally offered multi-tenant cloud and on-premises versions of their software are now switching to offering “private cloud” or “managed service” versions that are a hybrid of the previous approaches.

From what I can tell, this approach involves the vendor creating and managing a customer’s software instance, but doing so in a single-tenant model on the customer’s preferred cloud provider.

I’m curious to know how this works. Does the vendor get access the customer’s AWS/Azure/GC account and then create the resources to run the software there? Or does the vendor deploy the software in their own cloud accounts in the region/provider preferred by the customer, and then somehow keep the instance confined to being accessed within the customer’s network?

Example: https://document360.com/private-hosting/