It is currently not possible to dynamically change the log level in KRaft. For example:
kafka-configs.sh --bootstrap-server <address> --alter --add-config "kafka.server.ReplicaManager=DEBUG" --entity-type broker-loggers --entity-name 0
org.apache.kafka.common.errors.InvalidRequestException: Unexpected resource type BROKER_LOGGER.
The code to process this request is in ZkAdminManager.alterLogLevelConfigs(). This needs to be moved out of there, and the functionality has to be processed locally on the broker instead of being forwarded to the KRaft controller.
It is also an open question as to how we can dynamically alter log levels for a remote KRaft controller. Connecting directly to it is one possible solution, but that may not be desirable since generally connecting directly to the controller is not necessary. The ticket for this particular spect of the issue is https://issues.apache.org/jira/browse/KAFKA-13502