Managed Kubernetes – how do you manage those in your company?

Currently, there are multiple managed Kubernetes offerings out here. But lets take 3 major one for this case: AKS,EKS, GKE (in no particular order). Once your organization goes over 5-10+ clusters (there might be reasons for it) you get to the point where you need to have consistent things like:

* Different cloud providers have different configurations for baseline features (NetworkPolicies, ingress, CSI driver). How does one make sure they are consistent?

* RBAC - how do you manage RBAC consistently for all org with break-glass, ops/dev processes, joiners/leavers?

* Application deployments? Helm, Flux, etc. Tested, upgradable etc across the board.

* External resources like DNS, Storage, Databases, etc.

Few tried, some failed, and some succeeded. But projects are still there on the application layer more than anywhere else.

What is your stack to solve these problems?