Documentation clearly states to define "operand.image" in NodeFeatureDiscovery:
[-] https://docs.redhat.com/en/documentation/openshift_container_platform/4.21/html/specialized_hardware_and_driver_enablement/psap-node-feature-discovery-operator#psap-node-feature-discovery-operator-using-the-operator

This means that the version in "operand.image" needs to be updated as per newer OCP version.

There should be a dedicated steps to upgrade the operator which should contain a step to update the version in "operand.image" in NodefeatureDiscovery CR.

In case, defining "operand.image" is not necessary, then the config needs to be removed from existing OpenShift docs.

4.18-4.21 NFD Operator

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Tried creating NodeFeatureDiscovery CR and it got created even without defining "operand.image" and all the workloads started up fine.