|When old files are compressed by the Disk Cleanup, they are not moved to a special folder. They stay where they've always been but Windows just compresses them so they take up less space.|
"Old files" in that context are any files or applications which you have not used for a long time. So you would have to uninstall all such applications and delete all such files in order to for Disk Cleanup to show "zero" for compressed old files.
We cannot tell you what applications to uninstall or what files to delete. Only you know which ones you haven't used for long time.