OneDrive downloads all files just uploaded

sesslercory  That sounds backwards. OneDrive should be on your computer's internal drive and the backup software should copy that and anything else you want to the external drive.

I have 3 disc drives - 1 SSD for the o/s, and 2 HDDS for the data. I had moved OneDrive to the 1st of the two HDDs. I use Second Copy to nightly copy (anything that has changed) the entire contents of the 1st drive (the OneDrive folder and everything else on the 1st HDD) to the second HDD. That 2nd hard drive is never touched otherwise. And OneDrive does it's thing automatically all day long. Neither SecondCopy nor OneDrive mark any files - they are unaware of each other. Therefore I am tripple backed  up: the locale OneDrive, it's mirror in the cloud, and my 2nd HDD.
This has been my setup for probably 5 years now.