The game looks really cool, however if I had to give a bit of criticism, I think that it takes too long for the pinballs to start counting down then explode.
Based upon where I was getting lag-spikes, My guess is that was due to shader compilation. Basically whenever games render shaders, the engine needs to figure out how to render it and then cache it to a file. I was getting a spike during the first times it loaded a particle which, since particles are shaders, lines up with shader compilation issues. It's a pretty hard lag spike to fix because Godot needs to cache it to a file so every time it runs the shader it will be faster. If your game has loading screens then you can hide the particles behind a black screen but otherwise it's just a tricky bug to deal with.