I am using a multicloud application where all my K8s clusters from AWS, Azure are discovered and I can view my resources like Pods, Deployments from it so easier access.
For Private Only clusters, for the clusters to be discovered, I deployed a proxy pod on the cluster which is helping in traversing the data to my application. I am checking for ways to eliminate the use the proxy pod and let the clusters be discovered without much hassle. Hope my use-case is clear now.
You have a couple of options:
1) Enable the public API endpoint on your private clusters and restrict access using "control plane authorized networks"
2) Create a VPN connection between wherever your application is running and the VPC in which your clusters are running