A Microsoft file hosting and synchronization service.
Hi,TJ Fan
Welcome to Microsoft Community.
I understand that you want to backup the folders in your C drive.
You can choose which folders in OneDrive to synchronize, as shown in the window in the image you sent. However, the premise of selecting these folders is that the location of these folders needs to be in the OneDrive folder.
If you want to synchronize specific files, it is recommended that you copy the folder and paste this folder into the OneDrive folder so that OneDrive will start synchronizing these.
And, you need to use these files under the path of the OneDrive folder so that OneDrive can save the changes of these files at any time.
Note: Notice that the content you want to back up is in the C drive, which contains many system files. We only recommend that you use OneDrive to back up your private files without modifying system files. This is because modifying the paths to your system files may affect the use of your computer.
Please contact me if you need further assistance.
Best Regards,
Mila.L-MSFT| Microsoft Community Support Specialist