Still, if you find that you cannot open files with such brown box icon overlay, follow these suggestions to fix the isue on your Windows 11 PC: Unlink and Relink OneDrive/Dropbox.

To get the default Flip-3D icon, right-click on the new Flip-3D icon and select Properties. Then, under the Shortcut tab, open Change Icon. Next, under the location box, type C:\windows\explorer ...

If you want to revert a file or folder to its default icon, open its Get Info panel again, click the icon in the panel to select it, and choose Edit -> Cut or use the keyboard shortcut Command-X.