How do I get MY Documents folder back under "This PC" in explorer view tree?
Solution 1:
Right-click the OneDrive icon in the Notification area and click Settings. Click the Auto save tab. In Documents and Pictures, select This PC only for both Documents and Pictures. (REF: Files save to OneDrive in Windows 10)
If that doesn't help, you may have to reset the shell folder paths in the registry, as in Windows 10 User Shell Folders Restore Default Paths. (You need the registry fix #3, or refer to Table #2 for editing manually.)