How Can I Stop OneDrive Files from Syncing with SharePoint in My Organization?

Honestly, it seems like an X-Y problem. What's driving your desire to block this? If your main goal is to ensure files are in SharePoint for collaboration, focusing on training users to utilize SharePoint effectively might be more beneficial than trying to prevent OneDrive uploads.

OneDrive and SharePoint actually use the same infrastructure, which is why you're seeing that behavior. When users upload files to their OneDrive, they can still appear in SharePoint. It might seem like syncing is happening, but technically, it's different storage locations. To prevent this, you'll need to clarify your guidelines and consider revising the permissions. Perhaps educate users on directly using SharePoint instead.

It sounds like you're wanting to stop users from uploading files to their organizational OneDrive accounts, right? That's the root of the problem. You need to set up controls around OneDrive usage. Limit access or clarify that files should only be uploaded to specific SharePoint sites. This way, users won't get confused about where to store their documents.