I don't know much about html applications (or Godot honestly) but my immediate guesses on the main menu lag is either the music itself or or the invisible video player node from my original main menu which wouldn't play in browser. Since it's just a build I've tossed up for easy access, not sure if I'll fuss about fixing it since it doesn't seem to impede playing the game. I'll figure it out if I end up continuing development on it.
Thanks for the feedback! Glad you liked it.