Thanks for testing this. And yes, that's identical as far as I can see.
Other than that, I've created service accounts, added them to a group, and given the group access to the directory. I also have given the SA accounts Domain-wide Delegation to the Google Drive API (this to be able to impersonate on a users directory).
It's a GSuite (or Workspaces), and I'm the admin.
I've just tested with a brand new service account, but that gives the same errors.
What throws me off is that my account seems to have the correct permissions. It can both read and write without issues. So most of it works, but it's just halting on moving files to the backup drive afaik.
Also – the only thing I have changed on my end (rclone wise) is upgrading and changing the tps-limit against dropbox.
I'm also thinking permissions, maybe regarding something very specific. I have not made any changes to the permissions. Could Google have changed something (but then again, you should think other users would experience something similar).
I'll give it a go with --disable copy