Summary:
Quick Play opens the running world, not the game in the Game Menu, even if the window is not active. This leads to blocking the pointer within the boundaries of the background game window from which you can only exit by pressing the Windows button. This only works when fullscreen is disabled at startup.

Steps to reproduce:

1. Set the "fullscreen" switch in the settings to off.
   Don't use F11 as it doesn't save state on restart. --> MC-263865
2. Open the launcher and any other application (any: browser, calculator, notepad...) and maximize it.
3. Turn on the Quick Play feature.
4. Launch with Quick Play any of your worlds and immediately switch to a pre-opened application.
5. Wait 1 minute (while the world is loading).
6. Try to switch to the game without using the buttons.

Observed results:
The game started in the background and locked the pointer within the boundaries of its window.

Expected results:
The game will be put into pause mode (Game Menu) or the game window will appear on top of the open window.