On any Windows based system I've every touched the Windows Key is on the lowest row of keys, on the left, and very often the third key in (after a CTRL and FN key).

Any command for the browser must be done after the browser is open and its window has focus.  And WinKey+Up Arrow does maximize the window.

This is not, however, a browser specific command, but a Windows command.  Any window that happens to have focus will be maximized if you hit WinKey+Up Arrow, and will be restored down (not minimized to the system tray) if you hit WinKey+Down Arrow.

The list of Windows 10 (and other versions, too) Keyboard Shortcuts can be found at:  

Keyboard shortcuts in Windows - Windows Help

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Brian - Windows 10 Pro, 64-Bit, Version 2004, Build 19041  

The purpose of education is not to validate ignorance but to overcome it.
       ~ Lawrence Krauss