Ok, everyone I asked cant replicate it, so I've enabled the fullscreen button, that should fix it for you (The game will still be locked to the small size as it was only designed with that res in mind for time saving)
Yep, it works now. Weird issue. It might be a browser compatibility problem? I'm on Vivaldi, which shouldn't cause problems (it uses Chromium to render pages), but maybe the way the browser handles its UI drawing prevents it from getting focus for keys.
Yea that is weird, I use brave (also chromium based) but looking at the screenshots it looks like Vivaldi's UI is much more customized so I think you may be right. Do you have this problem on other WebGL games?