Before upgrading a TKGS workload cluster you should check its compatibility for upgrade. Compatibility must be checked against the TKG Service.

Verify Compatibility with TKG Service

Before upgrading a workload cluster you should check its compatibility for upgrade. If a cluster is incompatible with the TKG Service, upgrade the Tanzu Kubernetes release. Refer to the Release Notes for details on available TKrs. See also the online interoperability matrix.

You can list Tanzu Kubernetes releases and view their compatibility using following command. 
kubectl get tkr

The COMPATIBLE column indicates if that Tanzu Kubernetes release is compatible with the installed TKG Service. Starting with the TKG Service 3.1 release, the TYPE column returns compatibility status as well.

If you specify the TKGS cluster, you can view which TKr updates are available.

Using the v1alpha3 API: 
kubectl get tkc <tkgs-cluster-name>
Or, using the v1beta1 API: 
kubectl get cc <tkgs-cluster-name>
The UPDATES AVAILABLE column indicates if there is a Kubernetes upgrade available and the recommended next Tanzu Kubernetes releases to be used. For example: 
kubectl get tkc tkg2-cluster-11-tkc
NAME                  CONTROL PLANE   WORKER   TKR NAME                          AGE   READY   TKR COMPATIBLE   UPDATES AVAILABLE
tkg2-cluster-11-tkc   3               3        v1.25.7---vmware.3-fips.1-tkg.1   13d   True    True             [v1.26.5+vmware.2-fips.1-tkg.1]
There are two types of TKr formats: non-legacy and legacy.
  • Non-legacy TKrs are purpose-built for vSphere 8.x and are only compatible with vSphere 8.x
  • Legacy TKrs use a legacy format that is compatible with vSphere 7.x, and also with vSphere 8.x but for upgrade purposes only.
To list non-legacy TKrs: 
kubectl get -l !run.tanzu.vmware.com/legacy-tkr
To list legacy TKrs: 
kubectl get -l !run.tanzu.vmware.com/legacy-tkr