Hi @mark3,
Technically “sync to odrive” will do this, but it is a 1 to 1 mapping, as stated above. If you were to take the top-level folders on the external drive, place them into a subfolder, and then use “sync to odrive” on that it would achieve the goal of sync that data to your remote storage.
Realistically, sync may not the best solution for large volume hoarders (multi-terabyte levels); traditional backup is probably a better solution. I put some thoughts on that here in this post, if you are interested: Backup (one-way sync)