Some shortcuts on Ubuntu 18.04 are not editable in the Keyboard Shortcuts UI. For example the switch workspace to left or to right shortcut CTRL+ALT+LEFT or RIGHT. This shortcut is also useful when you programming in your IDE and you would like to navigate back and forward.

Here a workaround.
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# check current settings gsettings get org.gnome.desktop.wm.keybindings switch-to-workspace-left gsettings get org.gnome.desktop.wm.keybindings switch-to-workspace-right # disable shortcuts gsettings set org.gnome.desktop.wm.keybindings switch-to-workspace-left "['']" gsettings set org.gnome.desktop.wm.keybindings switch-to-workspace-right "['']" |