Biggest thing for us was converting all GPU particles to CPU. You can select a GPU particle node, then in the top middle of Godot click on GPUParticles2D and click "Convert to CPUParticles2D". But duplicate the GPU particle first, and have a global variable called "web_build: bool = true". Then in all scenes you have to put "if web_build == true, use CPU particle". There were some other things we did like object pooling but that was the biggest thing