Pressing Ctrl + Win sends the active object backward
If you have at least 2 objects on the artboard and the top one is selected, pressing Control + the Windows key on Windows 10 sends the active object backward one step. It's a keyboard shortcut that doesn't appear to be editable in Keyboard Shortcuts in case it interferes with that shortcut being used for something else.
Wow. Myra, this is something I'd never find. Nice catch! +10 points to the Gryffindor ;)