Like many here, I'm concerned about local backups. I have set all three of my OneDrive top level folders to "Always Keep on This Device". That has propagated to all subfolders. And I've verified that Time Machine and Carbon Copy Cloner both back up the folder at ~/Library/CloudStorage/OneDrive. So far, so good! My question is about what you said about the hidden cache folder, specifically "the file’s data will sometimes be retained in both the sync root and the cache, but the files will be linked using a clone, so they do not occupy any additional space.". When you've done as I've done (select Always Keep on This Device for first level folders within OneDrive), then can you count on local backups to get full copies of all files from ~/Library/CloudStorage/OneDrive?