The Mirantis Container Cloud GA release 2.21.1 is based on 2.21.0 and:
Introduces support for Mirantis Kubernetes Engine 3.5.5 with Kubernetes 1.21 and Mirantis Container Runtime 20.10.13 in the 12.x Cluster release series.
For details about the Container Cloud release 2.21.1, refer to its parent release 2.21.0:
Make sure to update the Cluster release version of your managed cluster before the current Cluster release version becomes unsupported by a new Container Cloud release version. Otherwise, Container Cloud stops auto-upgrade and eventually Container Cloud itself becomes unsupported.