Method 1: The "Alt + Enter" Shortcut (Try This First)
Most Unity games built for Windows support a universal toggle.
How to do it: Launch the game, wait for it to load, and press Alt + Enter.
Result: This usually snaps the game instantly from fullscreen to windowed mode. Pressing it again will revert it.
Method 2: Force Windowed Mode via Shortcut
If the keyboard shortcut doesn't work, you can modify the game's shortcut to tell the engine to start in windowed mode before it even launches.
Right-click the game's shortcut (e.g., on your Desktop) and select Properties.
Note: If you don't have a shortcut, right-click the game's .exe file, choose "Create Shortcut," and use that.
Locate the Target field. You will see the path to the game file ending in .exe".
Add a space after the quote, and then type:
-window-mode windowed
Example Target: "C:\Games\MyGame\Game.exe" -window-mode windowed
Click Apply and then OK.
Run the game using this specific shortcut.
Optional Flags:
If you want a specific size, you can add width and height commands:
-window-mode windowed -screen-width 1280 -screen-height 720