Problem: When trying to sync a SharePoint Online folder by clicking on the “Sync” button in the library toolbar, I got this error message:
Sorry, we can’t sync this folder, You’re already syncing a shortcut to a folder from this shared library.
Root cause: Apparently, this error indicates the particular SharePoint Folder or library is already under the OneDrive sync (or under any other folder which is already in sync)! So, to avoid double sync, the Microsoft OneDrive client displays this error message popup.
Solution: To resolve the issue, Login to the OneDrive (https://<<YourDomain>>-my.sharepoint.com) site and remove the Shortcut. Alternatively, you can Click on App launcher in the upper-left corner >> OneDrive >> My Files >> Delete the “chained” folder shortcut.
You can also leave the shortcut in OneDrive and access the Files from your OneDrive folder in File Explorer instead of establishing a new sync.
If the above solution doesn’t work, try unlinking your account from OneDrive (Log out from the OneDrive sync client), restart your PC, and then link it again to a new folder to re-establish the sync.