I have MATE on my Ubuntu computer but I have a little and simple problem. I play games in fullscreen and when I press Ctrl+Spacebar it uncaptures the mouse. How can I disable this function of Ctrl+Spacebar?
Go to System > Control Center and, in the filter bar, type 'Keyboard Shortcuts'. Click on the resulting configuration tool to open a new window listing all your keyboard shortcuts. Find the 'Ctrl+Space' shortcut, select it, and hit backspace. The shortcut will now be disabled.
I had Ctrl +Space set to "next input method" (whatever that means) in my IBus Preferences. It said space, so I took all that out and left it an empty field. The IBus Preferences is also called "Input Method" or "Keyboard Input Methods" in the MATE Control Center menus.