Is there an option to call callback script if something changed at destination after sync (no callback if nothing changed)?

Let me give you a modest personal opinion: the beauty of Rclone is its simplicity. Each new feature is also a potential point of failure.

Compare with Duplicati for example: excellent software, but very sophisticated (local databases, etc). Several headaches if you have to do a restore and the databases have corrupted.

Think of the simplicity of rsync …