As described in the official document you given in the post, “This feature (silently configure user accounts) works for computers that are joined to Azure Active Directory (Azure AD)”.
So if your computers didn’t join to Azure Active Directory (Azure AD), operations in the official document do not apply to you.
> everything the user has, is synced down on the client
<< Do you mean that you would like to sync files in OneDrive to the client or sync files in the client to OneDrive?
Currently, there maybe no related GPO to enforce files in OneDrive to be downloaded on the client.
If you would like to sync files in the client to OneDrive, redirecting and moving Windows known folders to OneDrive is the action closest to your needs.
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