I had the same issue of not being able to jump very high. I pulled out my Mac with a higher resolution, and the viewport scaled large enough to where I could jump. I had the same issue with my game. That the viewport would scale differently. It probably has to do with how Godot handles exporting to web, even though you can set a resolution during export and on Itch. Unsure of a fix around that though :/. But it was a great concept! Also bonus points because both of our games have King in the name! :)