Despite the options in the System Settings dialog for Keyboard Shortcuts, there are still several keybinds that are set outside of this. While you can set a keybind in the Keyboard Shortcuts screen, the pre-existing ones seem to take precedence, so the ones you defined don’t do what you’d like them to do.

As mostly a reminder post so I remember where they live each time I redo a system, here’s how to find the one(s) that  define keybindings I want to use (here’s looking at you Alt+F6):

  1. Install the dconf-editor package via the command:
    sudo apt-get install dconf-editor
  2. Open dconf-editor (when using Cinnamon, you should be able to search for it in the menus).
  3. Go to org > cinnamon > muffin > keybindings and adjust/remove the key bindings that conflict with the ones you set.

You may need to log out and log back in at this point to get the keybind to work (or run the command cinnamon –replace in a terminal).