Try this:
Find the game file (the .exe that starts the game). Right-click it > click "Create shortcut". Right-click the new shortcut > click "Properties". In the "Target" box, go to the end and add this: --windowed --resolution 1280x720 Example: "C:\Games\
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" --windowed --resolution 1280x720 Click Apply, then OK. Double-click the shortcut to launch the game. It should now open in windowed mode