Itch app cannot run webgl 2 zzz....
Tried on firefox and could run just fine, just some pointers:
When exporting, do it on release, you need to toggle the badly placed button on the lower right when saving the exported project, that will make it more light and faster.
Be more nice with your instakill elements, reducing a bit the hitbox will result in a better experience.
And add particles, lot of particles (I know is not a good advice for the current state of godot particles shader issues but keep that in mind).