Files and folders that appear only in OneDrive and not on drive C: are typically stored in the OneDrive sync folder rather than in the older locations previously used.
On Windows, the local OneDrive folder is usually under the user profile, for example:
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C:\Users\<username>\OneDrive (personal)
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C:\Users\<username>\OneDrive - <OrganizationName> (work or school)
Files shown in OneDrive on the web are synchronized with this local OneDrive folder, not with arbitrary locations on C:. If files were moved into OneDrive (for example, Desktop/Documents/Pictures were redirected into OneDrive, or folders were manually moved), they will no longer appear in their old locations on C: but instead under the OneDrive path above.
If a folder is shared with the account and added as a shortcut, it appears under My files in OneDrive on the web and in the OneDrive folder in File Explorer (for example, under OneDrive - Contoso). If it is not visible locally, selective sync might be enabled; in that case, enable the folder in OneDrive settings under Account → Choose folders so it syncs to the PC.
Note that OneDrive and Windows features such as Files On-Demand and Storage Sense require the OneDrive folder to be on the system partition (C:). OneDrive does not synchronize arbitrary folders elsewhere on C: unless they are inside the OneDrive directory or linked into it using supported methods.
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