public Optional<String> reasonNotLocallySupported(
        String featureName,
        short newVersion
    ) {
        return reasonNotSupported(newVersion,
            "Local controller " + nodeId,
            localSupportedFeature(featureName));
    }
A holder class of the local node's supported feature flags as well as the quorum node IDs.
metadata/src/main/java/org/apache/kafka/controller/QuorumFeatures.java