The OpenShift Container Platform 4.16 logging documentation includes a compatibility table listing tested and validated external log forwarding destinations (for example Elasticsearch and Logstash) in the “Log output types” section:

https://docs.redhat.com/en/documentation/openshift_container_platform/4.16/html-single/logging/logging#supported-log-outputs_logging-output-types

However, the Cluster Logging Operator 6.x documentation does not provide an equivalent table showing tested or validated versions of external log forwarding destinations (such as Elasticsearch, Logstash, Kafka, or Syslog):

https://docs.redhat.com/en/documentation/red_hat_openshift_logging/6.2/html-single/configuring_logging/index#cluster-logging-collector-log-forwarding-about_configuring-log-forwarding

As a result, it is unclear which external destination versions are supported or validated with Cluster Logging Operator 6.x.