18.04 Change shortcut for switching workspace

Solution 1:

The setting is available, but is not exposed in the user interface.

You can install dconf-editor to have a graphical interface to change a plethora of settings. The settings you are looking for are

org.gnome.desktop.wm.keybindings switch-to-workspace-down ['<Super>Page_Down', '<Control><Alt>Down']

and

org.gnome.desktop.wm.keybindings switch-to-workspace-up ['<Super>Page_Up', '<Control><Alt>Up']

You can change the assigned keys using dconf-edit. The settings can also be changed through the terminal with the command gsettings, e.g. the command

gsettings set org.gnome.desktop.wm.keybindings switch-to-workspace-down "['<Super>Page_Down', '<Control><Alt>Down', '<Alt>d']"

would add Alt+d as a shortcut key to switch to a workspace down.

One can reset a dconf setting to the factory default setting with gsettings reset, as in

gsettings reset org.gnome.desktop.wm.keybindings switch-to-workspace-down