Since MongoDB 7 (and perhaps even since 6) there's an issue that prevents moving large collections between databases by using

db.runCommand({renameCollection:'database1.a', to:'database2.a'})

It fails with an error message:
```

MongoServerError: batched writes must generate a single applyOps entry

```

Reading the logs refers that it tries to do it as a transaction and there's that infamous 16 MB limit or something that is met in case a  larger collection is being moved.