That would be surprising, the grass is entirely shader animated and pushed inside a Godot MultiMesh, making us able to render it in a single draw call, and our map being roughly 15x15 Godot units, there just isn't much geometry to compute. The game even runs on my phone from 2020 at 12 FPS,
We've also got others who have been praising the performance, so it is pretty confusing. Do you mind me asking what grade of Hardware you are using ? I'd love to be able to find possible causes and reasonable fixes for anyone trying to play, or learn something about optimization!