How do I get out of split screen mode when I never entered it completely? On occasion, when attempting to either go into fullscreen or maximize a window, I will accidentally trigger the split screen setup, where half of the desktop turns blue.  However, if the application doesn't support split screen, it gets stuck this way.  The top taskbar is gone, so there are no menus.  Cmd + Tab doesn't do anything.  Trying to drag any window into the blue area or the other side doesn't do anything, except maybe move the blue area from one side to the other.  The only fix I've found so far is to completely shut the machine off, as I can't log out (I just Googled and found a way to do so via CLI, but that's not intuitive for most).

Is there a way to either cancel split screen or successfully enter into split screen so that I can then exit?
Pressing Esc has worked for me. In High Sierra, the option is blocked in the first place, and in the case of no other windows supporting split screen you can click in the blurry area with no available windows.