According to ROX-8046 (need to verify this) even though spec.clusterName is required, it is possible to create a SecuredCluster CR without it, by omitting spec altogether.

IIRC we do fail validation in this case but it would be nice to give feedback earlier.
Perhaps it is possible to do this by making spec itself required?

Caveats about adding new required fields apply (not a backwards compatible change) but perhaps it could be acceptable (see CRD ratcheting) given that spec is in practice already required for the above reason. TBD if OLM will let such change through.