Thank you for your feedback on this game! Good to see a fellow Godot developer around these parts, this was the first 3D game we have made as well! :D
A number of the features which need to be fine-tuned have things we weren't able to adjust in time unfortunately, however we are looking into updating a copy of this game and potentially releasing a separate build over the next couple of months, I have taken notes of what you have suggested and we'll see what we can do.
May I ask what your PC specifications are? (Graphics Card, CPU etc) We weren't able to reproduce any issues in lagging on our end while testing, however we would like to know what you're working with for the game to lag the way you are experiencing.