According to the current Logging documentation (https://docs.openshift.com/container-platform/4.12/logging/log_collection_forwarding/log-forwarding.html#logging-create-clf_log-forwarding) we can observe that in "ClusterLogForwarder resource example" the parameter "serviceAccount" is not correct.

After checking the 5.8 multiCLF enablement (https://docs.google.com/presentation/d/1DOpnr4MpV89tM6Z0PgofvW0m3ZdPj3VtfSiLdW1zQCE/edit#slide=id.g275fa28b15a_0_13) and testing, the parameter is called "serviceAccountName"