There is a keydow/keyup conflict with the iframe-surrounding page. By opening "More tools >Developer Tools > Elements > Event Handlers" and then manually removing the itch.io keydown and keyup handlers, I was able to make it work. From my POV this is a serious hurdle and I have no clue how other games circumvent this problem. It is in effect really frustrating. Also, the exact same handler works in jack airbourne, but not here.... Are they allowing / disallowing handler override individually?