Thanks for the feedback! Unfortunately, this is an ITCH.IO issue: when you launch the game, you have to click on the screen with your mouse to activate the window.
The Game Boy uses 4 main buttons in addition to the D-pad: "A", "B", "Start", and "Select". In the games, you can use "Z" or "Alt" for the "A" button, "X" or "Ctrl" for the "B" button, "Enter" for "Start", and "Shift" for "Select".
