Since you mentioned a raspberry pi I suppose you are using Linux. In this case you can use root.attributes('-type', 'dock') (assuming your Tk instance is called root). This way, your window will have no decoration (so no close or minimize buttons) and will be always on top. If you don't want it always on top, you can use type 'splash' instead. In any case, you will need to use focus_force to be able to get keyboard focus.
import tkinter as tk
root = tk.Tk()