Can't find Alt-F5 in Settings/Keyboard Shortcuts

Solution 1:

"Restore", which is found in the Windows section in Settings - Keyboard shortcuts, is not only assigned to Super+Down, but also to the "traditional" shortcut Alt+F5. You can disable the binding to Alt+F5 and retain the Super+Down binding with the following command in the terminal or in the run dialog (Alt+F2):

gsettings set org.gnome.desktop.wm.keybindings unmaximize "['<Super>Down']"

That removes the assignment to Alt+F5, but maintains Super+Down for unmaximizing a window. Reset to the default (['<Super>Down', '<Alt>F5']) with the command

gsettings reset org.gnome.desktop.wm.keybindings unmaximize

You can edit this and many other "hidden" settings using dconf-editor, not installed by default.