I believe the hot key for that is F. If that doesn’t work, Alt+Enter works too.
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Yes. It is.
And it is apparently even sticky. I haven't played Morenatsu for the last few updates since it started full screen and there did not seem an option or a preference to run windowed every time.
Small thing but important for user interface for even stupid folks to know that it can be made to run windowed every time instead of wondering.
Please put the check box back. Thank you.