v.25.5Bug Fix (user-visible misbehavior in an official stable release)
IcebergS3 supports count optimization, but IcebergS3Cluster does
Official CH changelog text
IcebergS3 supports count optimization, but IcebergS3Cluster does not. As a result, the count() result returned in cluster mode may be a multiple of the number of replicas. #79844 (wxybear).