Hi, and welcome to Microsoft Q&A.
To keep files from syncing to OneDrive, ensure that the backup is disabled in Manage Backup:
If the backup continues to re-enable itself, you may want to reconsider storing your data in the Desktop, Documents, Pictures, Music, and Videos Standard folders, as these are the only folders that may be affected by OneDrive.
If you are backing up your files using a third-party program, consider storing the bulk of your data on a separate partition on the C: drive.
I hope that helps.
Craig