Duplicacy for streamed cloud to cloud backup without downloading?

I use Google Drive (GD) (streaming) and would like to back it up to B2 by directly streaming the data from GD to B2 without having to down- and upload everything.

That requires running the backup tool in the Google Cloud for example.

I’m wondering of Duplicacy could somehow be used for such a scenario? The idea would be to keep minimal backup state information, no caching at all, while still making use of deduplication, parallel transfers etc.

You could run duplicacy on the cloud instance, yes. You would need to mount your Google drive data, using e.g. rclone.