I feel like you offered me a gimmick platformer, and did a bait-and-switch giving me a fantastic one with tight controls and just-right levels.
I noticed it looks like you’re suffering from particle load lag when they first pop up on screen. This wasn’t solved AFAIK for web build in 4.0, but two solutions were provided by a dev here: https://forum.godotengine.org/t/handling-particle-shader-compilation-lag-in-godot-4-web-compatibility-renderer/36170/2