Opensearch stores the logs within indices and these will be stored under the path specified within the opensearch.yml. Indices are made up of shards and shards will be spread across the available Opensearch nodes within your cluster.
How the logs are stored within the journal and how they end up being stored within Opensearch are different and thus comparing isn’t very useful.
Mongo nodes will have the same folder structure and data as long as they are all members of the same replica set. Only the primary mongo node can be written to.