1 voteKent commented
All SyncToy needs is to be able to 'see' ALL of the files on your OneDrive cloud, not just the ones being synchronized to C: with OneDrive.
Huge numbers of people are upgrading to SSD's for their C drive now for performance reasons and offloading personal files to an internal or external large capacity drive. These files cannot be backed up with SyncToy because the cloud isn't visible to it. One Drive can't be used to do that because it would quickly overwhelm the fast, but small capacity SSD. This is a gaping hole in the capabilities of OneDrive and SyncToy. The C: centric nature of OneDrive and SyncToy kills its true potential. Solution: Google.