Starting in 3.6 we no longer replicated renameCollection across databases as its own oplog entry. Instead we log each component operation of the rename individually. 3.6 still needs to support applying those oplog entries to support someone who backs up a 3.4 replica set and wants to restore it to 3.6. But in 3.8+ we don't need to support interoperability with 3.4, so we should remove support for applying these types of oplog entries