In AKS, I think you can create the AKS clusters in the different subnets in the same vnet with an advanced network. For more details about the network, see Choose the appropriate network model. But it's not a perfect solution and there are some limitations for it. For example, the AKS clusters should be in the same region as the vnet.

You can take a look at Gotchas & Solutions Running a Distributed System Across Kubernetes Clusters. As it said, it's hard to communicate from different regions and nothing has yet solved the problem of running a distributed system that spans multiple clusters. It’s still a very hard experience that isn’t really documented.

So, maybe there would be a long time to wait for the perfect solution.