It’s a lot slower than mongodump / mongorestore & you are not saving the metadata so you will have to recreate the indexes manually. This solution is similar to mongodump / mongorestore but instead of using binary files (BSON), you are using plain text JSON files. It’s not 100% guaranteed that it works as you might find compatibility issues but I would give it a shot. You can just mongodump in 3.6 and restore in a brand new 4.4 cluster. The big bonus here is that you don’t have to care about recreating your indexes because they will be saved as well in the metadata & they will be rebuilt on the new cluster. But because 3.6 is not excessively old, it might work just fine. The BSON file they create might not be compatible if the gap between your MongoDB versions is too large (like 2.4 to 4.4 for example). Mongodump & mongorestore can backup and restore entire databases in a MongoDB cluster.

But before you try anything BACKUP EVERYTHING and of course make sure that you can recreate a 3.6.3 node from your backup so you can always come back and try something else.

Hi have multiple solutions to upgrade from MDB 3.6 to 4.4.

Upgrading from media shout 4 to 6