As far as I can tell. world_to_screen doesn’t exist. My guess is that ChatGPT suggested an old or incorrect function, or one that exists in another language which is a common occurrence with AI code. I would ask ChatGPT what that function is supposed to do and maybe get it to write out the function for you.
I don’t know how to make such an indicator but I found a couple of links on the subject by searching “Godot off-screen indicator”.