Microsoft is no longer treating the ‘3D Objects’ folder as a special folder in File Explorer. Windows 10 users can still access it directly from the %UserProfile% folder. The 3D Objects folder was created as a place to store all those 3D object files that Microsoft thought people would be downloading. However, most people did not find 3D Viewer as useful as Microsoft, and the most popular search query was how to remove it. Microsoft finally got the hint with yesterday’s release of Windows 10 Insider build 21322 in the Dev channel.
Source: https://www.bleepingcomputer.com/news/microsoft/microsoft-removes-3d-objects-windows-10s-most-useless-folder-from-file-explorer/