If your SDDC has a vSphere with Tanzu workload domain, after updating the vCenter Server instances, you update the vSphere with Tanzu clusters.
The Kubernetes software version is a string in the cluster manifest that is a semantic version notation in the form of x.y.z, where x is the major version, y is the minor version, and z is the patch version.
You cannot decrease the version. For example, you cannot downgrade from Kubernetes v1.17 to v1.16.
You can upgrade the minor version only incrementally. Skipping minor versions is not supported. For example, you can upgrade from Kubernetes v1.16 to v1.17, but you cannot upgrade from Kubernetes v1.16 to v1.18.
You cannot change the major version, such as upgrading from v1.16 to v2.0.
In this design you upgrade the Kuberenetes version from v1.16.8 to v1.18.5 incrementally.
Because Kubernetes v1.16.8 is incompatible with vSphere 7.0 Update 1, you cannot update the Supervisor cluster before updating the Tanzu Kubernetes cluster.
Review the supported update paths. See Supported Update Path in the vSphere with Tanzu Configuration and Management documentation.