Description:

There is a statement in Monitoring docs about fluentd, and it is available here:
 [-] https://docs.redhat.com/en/documentation/openshift_container_platform/4.19/html-single/monitoring/index#configuring-core-platform-monitoring:~:text=Fluentd,to%20different%20outputs. 

Fluentd has been removed starting RHOL 6.0.
RHOL5.y versions are not compatible with RHOCP starting 4.18 version.

The statement (along with deprecation note) needs to be removed from RHOCP 4.18 and 4.19 monitoring docs:

Fluentd
  Fluentd is a log collector that resides on each OpenShift Container Platform node. It gathers application, infrastructure, and audit logs and forwards them to different outputs. 

Additional Detail:

Fluentd has been replaced with Vector and that been references as log collector in the document link. So, fluentd section can be removed from  RHOCP 4.18 and 4.19 monitoring docs.