I found out that the separate Topic Operator configured through the Kafka.spec.topicOperator does not work anymore due to several issues which seem to be present for several releases. Since nobody reported it and this is deprecated for a long time anyway, I propose to remove it form the code instead of fixing it.

For more details, see the related Strimzi proposal: https://github.com/strimzi/strimzi-kafka-operator/pull/3091