If you are encountering Steam Destination folder must be empty message in Windows 11/10, use these solutions to fix the problem.

Read: Source and destination file names are the same when burning disc What does it mean when the destination folder is the same as the source folder?

This only happens when doing robocopy from a SYSTEM folder (My documents, My pictures, etc) but not when I create a non-system folder and copy the contents to a destination folder than I created.